The problems are region-specific. Honestly, there are no easy solutions.
Useful link:
https://www.jckonline.com/editorial-article/possible-know-jewelry-comes-from
Showing posts with label origin. Show all posts
Showing posts with label origin. Show all posts
Monday, October 21, 2019
Monday, October 07, 2019
Origin Determination Of Gemstones
Gubelin and the GIA are the best sources for origin determination.
Useful link:
https://www.gubelingemlab.com/en/gemlab/reference-collection
Useful link:
https://www.gubelingemlab.com/en/gemlab/reference-collection
Sunday, January 14, 2018
Saturday, February 13, 2016
Friday, February 05, 2016
Sunday, May 04, 2008
Paraiba Tourmaline Controversy
David Federman writes about the pros and cons with the origin name Paraiba + provenance issues and the impact @ http://www.colored-stone.com/stories/may08/paraiba.cfm
I think Dave Federman was spot on.
I think Dave Federman was spot on.
Tuesday, April 22, 2008
Origin, Ceylon Sapphire
I think the initiative by the Sri Lankan Gem & Jewelry Association to promote their colored stones, especially sapphires is a great idea + it will definitely popularize Sri Lankan sapphires worldwide but also position Sri Lanka on top of the pyramid provided the origin certification is done by a laboratory that is well-known, trusted and recognized worldwide + I don't think the local gem testing laboratories have the same luster like the international laboratories + my view is it makes sense to certify good quality stones of 1 carat and above.
Useful links:
www.facetssrilanka.com
www.srilankagemautho.com
www.ips.lk
Useful links:
www.facetssrilanka.com
www.srilankagemautho.com
www.ips.lk
Tuesday, May 22, 2007
A Question Of Origin: A Different View
(via Gemological Digest, Vol.3, No.1, 1990) Charles A Schiffman writes:
Relating a source to the presence of certain inclusions or other physical properties is not a recent idea, but goes back to the last century. A good example in the literature is found in Max Bauer’s Edelsteinkunde, 3rd edition, Tauchnitz Verlag, 1896/1932; the author points out the great importance of inclusions in determining origins (page 499) and goes on about their description.
In more recent times, in the Handbook Of Gem Identification by R.T.Liddicoat, 11th edition, GIA, 1981, typical inclusions related to sources are quoted (pages 88-89, 95-96).
Inclusions As A Means Of Gemstone Identification by E.Gubelin, GIA, 1953, has been the standard course book at the GIA on the matter of inclusions related to source.
That gemstones of certain sources were highly favored long ago is a historical fact, independent from gemology.
This writer recalls one merchant who was proud because he dealt only in Burma rubies that he bought directly from Burma, following requests from customers in the jewelry trade, and he was not an isolated case.
The trade has a strong demand for origins that is documented by the Definitions of the CIBJO (published about 1968) in Europe, a body grouping a majority of dealers and retailers. The following is extracted from CIBJO:
Art.2: Designation of color and place of origin (a) names of gem localities used heretofore to describe the color of gemstones, cannot be used any longer (b) indications of place of origin can be only added if the origin is known and can actually be corroborated. This proof may be given either by physical properties, or by the stone’s inclusions, in so far as they are characteristic of a definite area.
Obviously there are limitations to finding out origins, i.e the absence of characteristic features. For this reason, the origin of many specimens of such gemstones as garnet, tourmaline and quart cannot be found.
An interesting point is that considering these limitations, where no origin may be objectively ascertained, a lab sometimes faces little understanding in trade circles.
Answering the demand from the market for general testing and for determination of origin, Gubelin Laboratory extended its activities (previously only for the company’s own needs) to outside inquiries in the late 1960’s.
Time has not stood still since then. Investigation has become a challenge to go beyond routine methods, using more complex instrumentation. Even so, some limitations will remain in the feasibility of this complex and difficult task, in an effort to base it on objective methods.
On the other side, the gemologist familiar with this field is conscious of the big commercial assets involved by people chasing the rare and exceptional items. This attitude is a very human one, so that it is hard to believe that interested parties will just forget about demanding origin information.
Showing different aspect of the question in this magazine will hopefully lead to a better understanding of the parties concerned, to improve their cooperation and contribute to solving pending questions.
Relating a source to the presence of certain inclusions or other physical properties is not a recent idea, but goes back to the last century. A good example in the literature is found in Max Bauer’s Edelsteinkunde, 3rd edition, Tauchnitz Verlag, 1896/1932; the author points out the great importance of inclusions in determining origins (page 499) and goes on about their description.
In more recent times, in the Handbook Of Gem Identification by R.T.Liddicoat, 11th edition, GIA, 1981, typical inclusions related to sources are quoted (pages 88-89, 95-96).
Inclusions As A Means Of Gemstone Identification by E.Gubelin, GIA, 1953, has been the standard course book at the GIA on the matter of inclusions related to source.
That gemstones of certain sources were highly favored long ago is a historical fact, independent from gemology.
This writer recalls one merchant who was proud because he dealt only in Burma rubies that he bought directly from Burma, following requests from customers in the jewelry trade, and he was not an isolated case.
The trade has a strong demand for origins that is documented by the Definitions of the CIBJO (published about 1968) in Europe, a body grouping a majority of dealers and retailers. The following is extracted from CIBJO:
Art.2: Designation of color and place of origin (a) names of gem localities used heretofore to describe the color of gemstones, cannot be used any longer (b) indications of place of origin can be only added if the origin is known and can actually be corroborated. This proof may be given either by physical properties, or by the stone’s inclusions, in so far as they are characteristic of a definite area.
Obviously there are limitations to finding out origins, i.e the absence of characteristic features. For this reason, the origin of many specimens of such gemstones as garnet, tourmaline and quart cannot be found.
An interesting point is that considering these limitations, where no origin may be objectively ascertained, a lab sometimes faces little understanding in trade circles.
Answering the demand from the market for general testing and for determination of origin, Gubelin Laboratory extended its activities (previously only for the company’s own needs) to outside inquiries in the late 1960’s.
Time has not stood still since then. Investigation has become a challenge to go beyond routine methods, using more complex instrumentation. Even so, some limitations will remain in the feasibility of this complex and difficult task, in an effort to base it on objective methods.
On the other side, the gemologist familiar with this field is conscious of the big commercial assets involved by people chasing the rare and exceptional items. This attitude is a very human one, so that it is hard to believe that interested parties will just forget about demanding origin information.
Showing different aspect of the question in this magazine will hopefully lead to a better understanding of the parties concerned, to improve their cooperation and contribute to solving pending questions.
Monday, May 21, 2007
A Question Of Origin: A Different View
2007: Here is an interesting perspective on the question of origin from the father of inclusion studies.
(via Gemological Digest, Vol.3, No.1, 1990) Dr Eduard Gubelin writes:
The pros and cons of origin reports have been discussed on so many occasions during numerous conferences that I do not wish to repeat the arguments. Yet my strongest arguments in favor of origin reports are:
a) The fact that gemstones are very valuable and rare objects, and as such are entitled to be compared with objects of art and antiquity. It is customary that art and antique collectors request and receive a certificate of origin and authenticity. I see no reason why buyers of gemstones should not have the same right to ask for and obtain a certificate of origin and genuineness. The request for a certificate of origin need not necessarily be limited to the few precious gemstones (alexandrite, emerald, diamond, black opal, ruby and sapphire) but could be extended to the less expensive gemstones (beryls, chrysoberyls, peridot, quartz, topaz, tourmaline, spinel, etc). I have the feeling that my quite representative and comprehensive gem collection has been admired by all those prominent gemologists who have seen it because each individual specimen is marked with its origin. Why shouldn’t other buyers and collectors of gemstones be entitled to know the origin of their collector’s items? You know just as well I do that gemstones are among the items least commonly collected. Definitely much less than paintings, antiques, weapons, stamps or even such odd objects as hats, scarves and uniform buttons. Personally I am convinced that origin reports honestly and correctly stated would help a great deal to stimulate many more people to collect gemstones.
(b) My next argument in favor of origin reports is scientific: Of what value are the more recent and very profound investigations of, and publications on, original gem deposits such as those by Dr Hanni (about the emerald mines at Santa Terezinha da Goias, the emerald mine of Belmont near Itabira or the emerald deposit of Ankadilalana on Madagascar), or Dr Peter Keller’s research (on rubies from Mogok and those from Thailand), or my studies (of gem deposits of Sri Lanka, at Mogok, the jade occurrences in Northern Burma, and the gem deposits in Pakistan, and so son and so forth), if afterwards neither the authors of these studies nor other learned gemologists are allowed to profit from their intrinsic knowledge and experience? After all, the details in these very valuable articles about old and new gem deposits serve the purpose that gemstones occurring in the described deposits may be recognized as such by their particularities of origin. Thanks to Dr Hanni’ publications about emeralds from Santa Terezinha and those from Belmont, numerous interested gemologists are definitely capable of recognizing and distinguishing the emeralds from these two sources at first sight without any difficulty, and even discerning them from those originating, for instance, from Chivor or the Muzo area. Without bragging, I may emphasize that the staff of the Gubelin Laboratory under the directorship of Mr C A Schiffmann, as well myself, could very easily undertake such a distinction under the condition that the gemological properties agree with one or other of these well-known emerald deposits.
Your argument concerning the uranium pyrochlore inclusions in Pailin sapphires which have also been observed in Australian sapphires may seem to be correct, but it is not quite so, because in any scientific work, progress and new observations are made. Yet whenever a publication is made, the author can only state his knowledge at the time of writing. It is not his mistake if later on new discoveries are made, but he must be ready to correct his previously made incomplete or incorrect statement. Mr John Koivula did so in the Photoatlas of Inclusions In Gemstones. As a matter of fact, the text had already been typed when I learned that pyrochlore is also present in Australian sapphires. Consequently I not only corrected this statement, but presented further detailed knowledge by stating that urnanium pyrochlore is a frequent guest mineral in sapphires originating from a basaltic environment. Perhaps these arguments may enrich the discussion about this problem of origin reports.
(via Gemological Digest, Vol.3, No.1, 1990) Dr Eduard Gubelin writes:
The pros and cons of origin reports have been discussed on so many occasions during numerous conferences that I do not wish to repeat the arguments. Yet my strongest arguments in favor of origin reports are:
a) The fact that gemstones are very valuable and rare objects, and as such are entitled to be compared with objects of art and antiquity. It is customary that art and antique collectors request and receive a certificate of origin and authenticity. I see no reason why buyers of gemstones should not have the same right to ask for and obtain a certificate of origin and genuineness. The request for a certificate of origin need not necessarily be limited to the few precious gemstones (alexandrite, emerald, diamond, black opal, ruby and sapphire) but could be extended to the less expensive gemstones (beryls, chrysoberyls, peridot, quartz, topaz, tourmaline, spinel, etc). I have the feeling that my quite representative and comprehensive gem collection has been admired by all those prominent gemologists who have seen it because each individual specimen is marked with its origin. Why shouldn’t other buyers and collectors of gemstones be entitled to know the origin of their collector’s items? You know just as well I do that gemstones are among the items least commonly collected. Definitely much less than paintings, antiques, weapons, stamps or even such odd objects as hats, scarves and uniform buttons. Personally I am convinced that origin reports honestly and correctly stated would help a great deal to stimulate many more people to collect gemstones.
(b) My next argument in favor of origin reports is scientific: Of what value are the more recent and very profound investigations of, and publications on, original gem deposits such as those by Dr Hanni (about the emerald mines at Santa Terezinha da Goias, the emerald mine of Belmont near Itabira or the emerald deposit of Ankadilalana on Madagascar), or Dr Peter Keller’s research (on rubies from Mogok and those from Thailand), or my studies (of gem deposits of Sri Lanka, at Mogok, the jade occurrences in Northern Burma, and the gem deposits in Pakistan, and so son and so forth), if afterwards neither the authors of these studies nor other learned gemologists are allowed to profit from their intrinsic knowledge and experience? After all, the details in these very valuable articles about old and new gem deposits serve the purpose that gemstones occurring in the described deposits may be recognized as such by their particularities of origin. Thanks to Dr Hanni’ publications about emeralds from Santa Terezinha and those from Belmont, numerous interested gemologists are definitely capable of recognizing and distinguishing the emeralds from these two sources at first sight without any difficulty, and even discerning them from those originating, for instance, from Chivor or the Muzo area. Without bragging, I may emphasize that the staff of the Gubelin Laboratory under the directorship of Mr C A Schiffmann, as well myself, could very easily undertake such a distinction under the condition that the gemological properties agree with one or other of these well-known emerald deposits.
Your argument concerning the uranium pyrochlore inclusions in Pailin sapphires which have also been observed in Australian sapphires may seem to be correct, but it is not quite so, because in any scientific work, progress and new observations are made. Yet whenever a publication is made, the author can only state his knowledge at the time of writing. It is not his mistake if later on new discoveries are made, but he must be ready to correct his previously made incomplete or incorrect statement. Mr John Koivula did so in the Photoatlas of Inclusions In Gemstones. As a matter of fact, the text had already been typed when I learned that pyrochlore is also present in Australian sapphires. Consequently I not only corrected this statement, but presented further detailed knowledge by stating that urnanium pyrochlore is a frequent guest mineral in sapphires originating from a basaltic environment. Perhaps these arguments may enrich the discussion about this problem of origin reports.
Friday, May 18, 2007
A Question Of Origin: A Different View
(via Gemological Digest, Vol.3, No.1, 1990) Grahame Brown writes:
Your well documented arguments against using origin reports to support price premiums for selected colored stones, should stimulate gemologists to think this very real problem through, rather than dismissing your arguments as being commercially unrealistic, or worse still, acquiescing to the rather dubiously based status quo.
Personally, I fully support the general thrust of your arguments, and wish to raise several additional points for consideration.
1. Researchers, species collectors and investors, excepted, why do human beings purchase colored stones? Surely the major factor influencing the desirability and subsequent purchase of a colored stone must be those visual characteristics contributing to the particular gem’s beauty and rarity. It is a fact that geography has little proven influence over the appearance of a colored stone.
2. Why should the presence of any visually detectable inclusion (s) in a colored stone not logically degrade, rather than sometimes upgrade, the value of the stone? Clarity should be a significant determinant of value; the country of origin of the gemstone’s inclusion should not practically influence its global value.
3. If origin reports are of such significance to the value of colored stones, why are these not routinely prepared for all colored stones?
4. If the gemologist wishes, or is forced by perceived necessity, to issue an origin report for a particular colored stone, then what data does he or she have to support their assignment of origin to that colored stone? The factual answer to this question is……precious little. Certainly, several most useful photoatlases of gemstone inclusions have been published, but none of these present an exhaustive review of characteristic inclusions found in colored stones from all past or present mines. This comparative information is essential if the origin of a colored stone is to be determined with any degree of accuracy. Yes, systematic collections of colored stones do exist, e.g. the GIA’s reference collection, but this collection is not readily accessible to an antipodean gemologist, who may be attempting to determine the origin of a troublesome colored stone. Excellent though the GIA reference collection is….is still incomplete. Perhaps the most striking inadequacy of gemology’s knowledge of characteristic gemstone inclusions is the fact that less than 50 per cent (author’s estimate) of the world’s colored stone deposits have been described, in any way, in the gemological literature. Simply put, insufficient data exists to allow error-free origin reports to be issued by the majority of gemologists.
Origin reports for colored stones may be economic necessity for some gemologists, but to me (for the reasons expressed above) they mostly represent quasi-scientific gemological humbug.
Your well documented arguments against using origin reports to support price premiums for selected colored stones, should stimulate gemologists to think this very real problem through, rather than dismissing your arguments as being commercially unrealistic, or worse still, acquiescing to the rather dubiously based status quo.
Personally, I fully support the general thrust of your arguments, and wish to raise several additional points for consideration.
1. Researchers, species collectors and investors, excepted, why do human beings purchase colored stones? Surely the major factor influencing the desirability and subsequent purchase of a colored stone must be those visual characteristics contributing to the particular gem’s beauty and rarity. It is a fact that geography has little proven influence over the appearance of a colored stone.
2. Why should the presence of any visually detectable inclusion (s) in a colored stone not logically degrade, rather than sometimes upgrade, the value of the stone? Clarity should be a significant determinant of value; the country of origin of the gemstone’s inclusion should not practically influence its global value.
3. If origin reports are of such significance to the value of colored stones, why are these not routinely prepared for all colored stones?
4. If the gemologist wishes, or is forced by perceived necessity, to issue an origin report for a particular colored stone, then what data does he or she have to support their assignment of origin to that colored stone? The factual answer to this question is……precious little. Certainly, several most useful photoatlases of gemstone inclusions have been published, but none of these present an exhaustive review of characteristic inclusions found in colored stones from all past or present mines. This comparative information is essential if the origin of a colored stone is to be determined with any degree of accuracy. Yes, systematic collections of colored stones do exist, e.g. the GIA’s reference collection, but this collection is not readily accessible to an antipodean gemologist, who may be attempting to determine the origin of a troublesome colored stone. Excellent though the GIA reference collection is….is still incomplete. Perhaps the most striking inadequacy of gemology’s knowledge of characteristic gemstone inclusions is the fact that less than 50 per cent (author’s estimate) of the world’s colored stone deposits have been described, in any way, in the gemological literature. Simply put, insufficient data exists to allow error-free origin reports to be issued by the majority of gemologists.
Origin reports for colored stones may be economic necessity for some gemologists, but to me (for the reasons expressed above) they mostly represent quasi-scientific gemological humbug.
Thursday, May 17, 2007
A Question Of Origin
2007: I think John Koivula was right. The laboratories have no need for origin, and in some cases there is no way of knowing where the stones came from.
(via Gemological Digest, Vol.3, No.1, 1990) John Koivula writes:
With regard to your article, “A Question of Origin,” I agree with your basic premise that where determining country of origin in a gem is concerned, there is some truth in the saying ignorance is bliss. The more knowledge one gains on this subject, the more complex the problem of geographical origin becomes. While an experienced, knowledgeable inclusion expert can identify country of origin for some stones, in most cases it is impossible to determine the precise country of origin. The inclusion identification work that is done by a few colleagues and myself at GIA is done as a scientific endeavor to expand our knowledge of gems—not to prepare country of origin reports.
Your statement that ‘consumer could then be told honestly that these (origin reports) are intended for collectors and researchers’ is part incorrect, because most researchers have no need for origin reports of the type produced by the various gemological laboratories that issue them. Most inclusion researchers study the stones themselves and draw information from the various professional gemological and other earth science publications. In the 25 years that I have done research in this field, I have never found a need for an origin report.
With regard to your comments on there being more than one sapphire mining area in the State of Montana, please be assured that when Dr Gubelin and I discuss inclusions in sapphires from Yogo Gulch in the Photoatlas, we are most definitely referring to stones from that specific locality. Also, in your discussion of Kashmir sapphires you state: “Since the mine is (and has been for many years) off-limits to foreigners, the question arises as to where gemologists got the study samples.” You fail to mention or reference, however, a relatively recent major article on the Kashmir deposit in which the authors obtained their information and samples first-hand at the mining area (D. Atkinson and R. Kothawala, “Kashmir Sapphire,” Gems & Gemology, Vol.19, No.2, 1983, pp 64-76). For some interested in scientific research on Kashmir sapphires, a 1983 article would seem to be at least as valuable as one published in 1890—especially considering the technological advances that have occurred in the interim. I am sure the gemological community is also looking forward to the results of your research on the 1 kg (5000 carats) of known Kashmir sapphire rough you had the good fortune to obtain.
(via Gemological Digest, Vol.3, No.1, 1990) John Koivula writes:
With regard to your article, “A Question of Origin,” I agree with your basic premise that where determining country of origin in a gem is concerned, there is some truth in the saying ignorance is bliss. The more knowledge one gains on this subject, the more complex the problem of geographical origin becomes. While an experienced, knowledgeable inclusion expert can identify country of origin for some stones, in most cases it is impossible to determine the precise country of origin. The inclusion identification work that is done by a few colleagues and myself at GIA is done as a scientific endeavor to expand our knowledge of gems—not to prepare country of origin reports.
Your statement that ‘consumer could then be told honestly that these (origin reports) are intended for collectors and researchers’ is part incorrect, because most researchers have no need for origin reports of the type produced by the various gemological laboratories that issue them. Most inclusion researchers study the stones themselves and draw information from the various professional gemological and other earth science publications. In the 25 years that I have done research in this field, I have never found a need for an origin report.
With regard to your comments on there being more than one sapphire mining area in the State of Montana, please be assured that when Dr Gubelin and I discuss inclusions in sapphires from Yogo Gulch in the Photoatlas, we are most definitely referring to stones from that specific locality. Also, in your discussion of Kashmir sapphires you state: “Since the mine is (and has been for many years) off-limits to foreigners, the question arises as to where gemologists got the study samples.” You fail to mention or reference, however, a relatively recent major article on the Kashmir deposit in which the authors obtained their information and samples first-hand at the mining area (D. Atkinson and R. Kothawala, “Kashmir Sapphire,” Gems & Gemology, Vol.19, No.2, 1983, pp 64-76). For some interested in scientific research on Kashmir sapphires, a 1983 article would seem to be at least as valuable as one published in 1890—especially considering the technological advances that have occurred in the interim. I am sure the gemological community is also looking forward to the results of your research on the 1 kg (5000 carats) of known Kashmir sapphire rough you had the good fortune to obtain.
Inclusions As Criteria In Gemstone Origin Reports
2007: The amazing thing is despite the limitations, the trade still insists for origin certification and a few gem testing laboratories are more than happy to provide their services at a cost.
(via Gemological Digest, No.3, No.1, 1990) Edwin Roedder writes:
Richard W Hughes has asked for my comments on the question of the use of gemstone origin reports and in particular on his paper on that subject in this same issue. As a mineralogist-geochemist who has only seen the fringes of the field of gemology over the years, it is not appropriate for me to discuss the uses being made of origin reports in the gem trade. I can only say that Mr Hughes paper seems to present a very coherent, well-documented and cogent review of the subject. Although I have read many scientific papers dealing with the inclusions in gems and the possibility of their use in determining origin, I have never seen an actual origin report, and hence my only comments deal the validity of the inclusions criteria that might be used in issuing any such report. These comments are quite apart from the difficulties mentioned by Mr Hughes of obtaining material of verifiable origin on which to establish such criteria.
I will discuss two aspects: first, the effects of the inherent variation in the inclusion population in samples from a given locality, and second, the general similarity of the inclusion populations in samples from many different localities.
Variation of the inclusion parameters within samples from a given locality
Many different kinds of inclusions, both fluid and solid, can be trapped in a given mineral from a given locality. The reasons for this wide range lie in the basic nature of the origin of inclusions. Primary inclusions formed during the growth of the host crystal, can trap any solid, liquid, or vapor phases that happen to be present at the time of growth. The much more common secondary inclusions are trapped as a result of healing of fractures in the host crystal that form at some later time; this later time may be immediately after completion of the growth of the host crystal, or as much as billions of years later.
Although I have studied a number of gem minerals, the bulk of my inclusion work has been on non-gem materials, but I am certain that the principals involved in the two types of materials are identical; the only real difference is in the rarity of gem minerals, and in the necessarily low abundance of inclusions in high quality stones. When I study the inclusions in many samples of a given mineral from a given locality (personally collected so there is no ambiguity as to sample origin), I usually find a large range in inclusion types, habits, and compositions in the different samples. The primary solid inclusions represent the trapping of those other solid phases that just happened to be present at the time of growth and which were enclosed rather than pushed aside by the growing crystal. If different solid phases were present in different part of the deposit, the solid inclusions that are trapped will differ similarly. Even the fluid that is trapped in primary inclusions can show gross differences in composition between the core and rim of a single host crystal, if the conditions have changed during that growth. Since some of the larger crystals in metamorphic rocks have recently been shown to have grown at rates in the range of only a millimeter in a million years, it would not be surprising to find that the composition of the fluids bathing the crystal had changed during its growth.
Secondary fluid inclusions (i.e most of the inclusions making up the feathers, etc in gems), represent one or more periods of fracturing and rehealing of the host crystal. It is very common to find that such fracturing has occurred at several different times, perhaps millions of years apart, and in the presence of very different fluids. So two different feathers in a single crystal may contain very different fluids.
Since such wide variations in the inclusions in different crystal or parts of a crystal from a single locality are so common, it may be difficult or even impossible to set up inclusion criteria that would permit a valid origin report to be written for a single sample of the host mineral from that locality. Various specific inclusion parameters seen in the single sample may match features seen commonly in other crystals from that same locality, but the wide range of possible parameter values, and the all-too-common atypical inclusions diminish the degree of confidence in any assignment of the sample to that locality. Although my work involves learning about the inclusions in samples from known localities, I would find it exceedingly difficult to have to work in reverse, as the gemologist must, and identify the locality of origin by the study of inclusions in a given sample. If presented with a single sample from one of the many localities I have studied, I might be able to venture an educated guess as to one (or more, as detailed below) possible localities, and in most cases I could say with some confidence that certain other localities were impossible, but I could not go beyond that. Perhaps in the future, when far more inclusion parameters can be determined with increased precision, this basic uncertainity might be reduced. Thus non-destructive chemical (and isotopic) analyses of the minor and trace elements in the fluids of inclusions might provide fingerprints that will greatly reduce the ambiguity in the assignment of origin, but will never eliminate.
Similarity of inclusion populations in samples from different localities
Gemstones, just as other natural crystals, have crystallized in a variety of geological environments, but even so, there is a relatively limited range for any given gem. Thus most gem quality corundums have formed in only a very few limited types of environment, such as certain slowly cooled igneous and metamorphic rocks. As a result, the overall range in composition of their inclusions, both solid and liquid is limited. A relatively rare phase as a solid inclusion may be a valuable but not necessarily unique indicator, e.g. the uranium pyrochlore referred to in Pailin sapphires. But many solid inclusions are of common minerals that might be expected in many localities, particularly in localities that are already similar geologically in virtue of the fact that a given gemstone is found in each. (On the other hand, certain solid inclusions can effectively exclude specific geologic environments. Thus fine fibrous amphibole inclusions are not expected in stones from a magmatic or high temperature metamorphic environment.)
Similarly, liquid inclusions in most minerals normally contain water + salt + CO2 major components. The amounts of the latter two may vary widely. For many years it was generally accepted that emeralds containing highly saline inclusions (i.e a saturated water solution plus a daughter crystal of NaCl) came from Colombian emeralds, but since then similar inclusions have been described in emeralds from other localities. CO2 is a major component in the fluid inclusions in many rock types that bear gem corundum and hence is not definitive of any specific locality.
If all the above caveats seem unduly pessimistic a to the significance of origin reports, please note that I have described only one of the many parameters that may be involved in judging the origin of a stone; I am not qualified to discuss color and its distribution and possible modification, fluorescence, density, refractive index, etc.
In closing, let me add one additional caveat. Origin reports must distinguish between synthetic and natural stones, as this is far greater importance in commerce than the difference between different localities, large as these are. In the past, the inclusions in gems have provided reliable criteria for differentiating. Synthetic stones generally had types of inclusions that were uncharacteristic of those from nature, and did not contain those that were characteristic of the natural stones. These differences are caused by the use of entirely different growth processes and conditions in the laboratory than were used in nature. Thus the manufacture of large corundum crystals in various colors by flame fusion provides high quality material for pennies per carat.
But it should be noted that the huge differences in value compared with natural stones provides a great incentive to eliminate these recognizable differences in the final product. Once careful study shows the nature of the inclusions present in (and believed to be characteristic of) the natural stones, it is highly likely that attempts will be made to grow synthetic stones by processes such that the inclusions will also appear natural. Presently available laboratory equipment can duplicate the pressure, temperature, and chemical environment under which any gem has formed in nature. This has been done with emeralds, which have been grown synthetically with strongly saline inclusions, and I have no reason to doubt that other natural appearing gems will be similarly produced and sold, if they have not been already.
(via Gemological Digest, No.3, No.1, 1990) Edwin Roedder writes:
Richard W Hughes has asked for my comments on the question of the use of gemstone origin reports and in particular on his paper on that subject in this same issue. As a mineralogist-geochemist who has only seen the fringes of the field of gemology over the years, it is not appropriate for me to discuss the uses being made of origin reports in the gem trade. I can only say that Mr Hughes paper seems to present a very coherent, well-documented and cogent review of the subject. Although I have read many scientific papers dealing with the inclusions in gems and the possibility of their use in determining origin, I have never seen an actual origin report, and hence my only comments deal the validity of the inclusions criteria that might be used in issuing any such report. These comments are quite apart from the difficulties mentioned by Mr Hughes of obtaining material of verifiable origin on which to establish such criteria.
I will discuss two aspects: first, the effects of the inherent variation in the inclusion population in samples from a given locality, and second, the general similarity of the inclusion populations in samples from many different localities.
Variation of the inclusion parameters within samples from a given locality
Many different kinds of inclusions, both fluid and solid, can be trapped in a given mineral from a given locality. The reasons for this wide range lie in the basic nature of the origin of inclusions. Primary inclusions formed during the growth of the host crystal, can trap any solid, liquid, or vapor phases that happen to be present at the time of growth. The much more common secondary inclusions are trapped as a result of healing of fractures in the host crystal that form at some later time; this later time may be immediately after completion of the growth of the host crystal, or as much as billions of years later.
Although I have studied a number of gem minerals, the bulk of my inclusion work has been on non-gem materials, but I am certain that the principals involved in the two types of materials are identical; the only real difference is in the rarity of gem minerals, and in the necessarily low abundance of inclusions in high quality stones. When I study the inclusions in many samples of a given mineral from a given locality (personally collected so there is no ambiguity as to sample origin), I usually find a large range in inclusion types, habits, and compositions in the different samples. The primary solid inclusions represent the trapping of those other solid phases that just happened to be present at the time of growth and which were enclosed rather than pushed aside by the growing crystal. If different solid phases were present in different part of the deposit, the solid inclusions that are trapped will differ similarly. Even the fluid that is trapped in primary inclusions can show gross differences in composition between the core and rim of a single host crystal, if the conditions have changed during that growth. Since some of the larger crystals in metamorphic rocks have recently been shown to have grown at rates in the range of only a millimeter in a million years, it would not be surprising to find that the composition of the fluids bathing the crystal had changed during its growth.
Secondary fluid inclusions (i.e most of the inclusions making up the feathers, etc in gems), represent one or more periods of fracturing and rehealing of the host crystal. It is very common to find that such fracturing has occurred at several different times, perhaps millions of years apart, and in the presence of very different fluids. So two different feathers in a single crystal may contain very different fluids.
Since such wide variations in the inclusions in different crystal or parts of a crystal from a single locality are so common, it may be difficult or even impossible to set up inclusion criteria that would permit a valid origin report to be written for a single sample of the host mineral from that locality. Various specific inclusion parameters seen in the single sample may match features seen commonly in other crystals from that same locality, but the wide range of possible parameter values, and the all-too-common atypical inclusions diminish the degree of confidence in any assignment of the sample to that locality. Although my work involves learning about the inclusions in samples from known localities, I would find it exceedingly difficult to have to work in reverse, as the gemologist must, and identify the locality of origin by the study of inclusions in a given sample. If presented with a single sample from one of the many localities I have studied, I might be able to venture an educated guess as to one (or more, as detailed below) possible localities, and in most cases I could say with some confidence that certain other localities were impossible, but I could not go beyond that. Perhaps in the future, when far more inclusion parameters can be determined with increased precision, this basic uncertainity might be reduced. Thus non-destructive chemical (and isotopic) analyses of the minor and trace elements in the fluids of inclusions might provide fingerprints that will greatly reduce the ambiguity in the assignment of origin, but will never eliminate.
Similarity of inclusion populations in samples from different localities
Gemstones, just as other natural crystals, have crystallized in a variety of geological environments, but even so, there is a relatively limited range for any given gem. Thus most gem quality corundums have formed in only a very few limited types of environment, such as certain slowly cooled igneous and metamorphic rocks. As a result, the overall range in composition of their inclusions, both solid and liquid is limited. A relatively rare phase as a solid inclusion may be a valuable but not necessarily unique indicator, e.g. the uranium pyrochlore referred to in Pailin sapphires. But many solid inclusions are of common minerals that might be expected in many localities, particularly in localities that are already similar geologically in virtue of the fact that a given gemstone is found in each. (On the other hand, certain solid inclusions can effectively exclude specific geologic environments. Thus fine fibrous amphibole inclusions are not expected in stones from a magmatic or high temperature metamorphic environment.)
Similarly, liquid inclusions in most minerals normally contain water + salt + CO2 major components. The amounts of the latter two may vary widely. For many years it was generally accepted that emeralds containing highly saline inclusions (i.e a saturated water solution plus a daughter crystal of NaCl) came from Colombian emeralds, but since then similar inclusions have been described in emeralds from other localities. CO2 is a major component in the fluid inclusions in many rock types that bear gem corundum and hence is not definitive of any specific locality.
If all the above caveats seem unduly pessimistic a to the significance of origin reports, please note that I have described only one of the many parameters that may be involved in judging the origin of a stone; I am not qualified to discuss color and its distribution and possible modification, fluorescence, density, refractive index, etc.
In closing, let me add one additional caveat. Origin reports must distinguish between synthetic and natural stones, as this is far greater importance in commerce than the difference between different localities, large as these are. In the past, the inclusions in gems have provided reliable criteria for differentiating. Synthetic stones generally had types of inclusions that were uncharacteristic of those from nature, and did not contain those that were characteristic of the natural stones. These differences are caused by the use of entirely different growth processes and conditions in the laboratory than were used in nature. Thus the manufacture of large corundum crystals in various colors by flame fusion provides high quality material for pennies per carat.
But it should be noted that the huge differences in value compared with natural stones provides a great incentive to eliminate these recognizable differences in the final product. Once careful study shows the nature of the inclusions present in (and believed to be characteristic of) the natural stones, it is highly likely that attempts will be made to grow synthetic stones by processes such that the inclusions will also appear natural. Presently available laboratory equipment can duplicate the pressure, temperature, and chemical environment under which any gem has formed in nature. This has been done with emeralds, which have been grown synthetically with strongly saline inclusions, and I have no reason to doubt that other natural appearing gems will be similarly produced and sold, if they have not been already.
Friday, May 11, 2007
Reliability Of Origin Determination For Gemstones
(via Gemological Digest, Vol.3, No.1, 1990) Dr Henry A Hanni writes:
Definition: Origin = geographical place where a gemstone is situated.
This is either the primary deposit in the parent rock or a secondary deposit where the gemstones have been accumulated after decomposition of the parent rock. Since the term Burma, Pailin and Kashmir have a geographical meaning, they should not be used to express a gemstone color type, because it is common knowledge that a particular deposit may produce different shades of colors, some of which may be found in other deposits, as well.
The need for certification of a gemstone’s origin seems to be limited to only a few species or varieties of gems, and to a small group of quite famous deposits. In certain cases, a cut stone can express its place of origin through its physical and chemical properties and by its inclusions and growth structure, as long as these are clearly distinguishable from all other types. Thus these properties must be unique, either alone or in combination. The greater the number of individual and characteristic properties found in a particular stone, the more reliable is the determination of origin. Valuable characteristics should not only positively testify to a certain origin, but the same time excludes other origin possibilities.
Because of the above, experts involved in origin determination must be aware not only of the properties and characteristics of gems from famous sources, but of the properties and characteristics of all other similar sources. Only the exclusive features, those which are unique to a particular deposit can be called diagnostic properties.
Depending on the complexity of the formation of the gem crystals and on the geologic environment, the type and number of characteristics can be quite varied. Formation of gems requires some indispensable main conditions without which the gem cannot grow, as well as side conditions which can influence the growth but are not essential to the growth. Some of these main and minor conditions which can influence the properties and characteristics of gems include:
- availability of the main constituent chemical elements, and the growth speed.
- the types of available trace elements, and their concentrations.
- transport processes and the transport media involved.
- the type of energy source involved in formation (intrusive pegmatite, metamorphic, etc.)
- pressure from free oxygen.
- cooling rate after formation.
- deformation history of the parent rock and the growing crystal.
- protogenetic inclusions, reflecting the parent rock.
- syngenetic inclusions, reflecting the transport medium and genetic formation type.
All of these factors can influence the individual characteristics of a gemstone crystal, resulting in differences in:
- the size and shape of crystals, and their growth zoning.
- color, color homogeneity, color variations.
- trace element mixture (including invisible trace elements).
- solid inclusions and twinning.
- the state of healed fissures (i.e. fingerprints), geometry and degree of restoration.
- nature of fillings in negative crystal voids.
- composition of fluid inclusions.
What sort of diagnostic origin information can we collect from a cut gemstone?
Characteristic features:
- Microscopic investigation
Color and growth zoning relative to the crystallographic structure, color inhomogeneity, twinning type (s), internal strain, observation of type and distribution of solid and fluid/gas inclusions, type of healing fissures.
- Physical and optical properties
Specific gravity, refractive indices, double refraction (birefringence), fluorescent behavior, absorption spectroscopy (UV, VIS, IR), spin resonance spectroscopy, composition of fluids and minimum temperature/pressure estimation (heat/freezing stage microscope).
- Chemical determination
Trace element determination by energy dispersive x-ray fluorescence analysis (EDS-XFA), amount or relative ratio of trace elements present (e.g. Ti, Fe, Cr, V, Ga, etc.), chemical analysis of inclusions by electron beam instruments (scanning electron microscope, electron microprobe).
Some of the observed and collected characteristics are not restricted to a certain deposit, but in combination may be of diagnostic value. Those observations which are unique for a special deposit are the most important diagnostic features in regard to origin determination. Successful origin determination involves the following steps:
Observation → Comparison → Interpretation
↑ ↑ ↑
Scrutiny Comprehension Prudence
How can we get reliable basic knowledge about materials of definite known origin?
The most simple answer to this question is to collect samples directly at the mine or source. In many cases, though, this is not possible, since the source may be exhausted, or located in an inaccessible location. Therefore we must collect our reference material from a safe source, like a museum, an old collection, etc. Information on gemstone sources can also be obtained from books and publications. Many historical gemstone sources are discussed in reference books. Geographical maps give specific information on the type of deposit, scientific publications reveal the properties of the respective material, chemical analyses of the gemstones and their inclusions are published. All observations must be in agreement with the known facts, e.g. trace elements with spectroscopic analyses, inclusions with geology, etc.
From all this information we gain a very complex view of a gemstone deposit and its production. The more material we investigate, the more dense our network becomes. We are even able to add new observations to the earlier information, building upon it. Sharing and discussing new information with knowledgeable colleagues in the same field provides an added check to our results. But it is still important to revise and recheck the fundamentals of the science by basic research and study of the literature for information on new sources and new techniques. Stagnation is dangerous.
Limitations in the determination of origin
As I have pointed out at the beginning, we use differences in properties as a means of discrimination. Properties which are repeated in stones from more than one source are not valued as diagnostic characteristics, but can nevertheless be helpful in excluding other localities which do not possess these properties. As an example, a certain shade of blue does not prove a certain origin, nor does a misty turbidity. But the misty turbidity in combination with the absence of rutile needles points towards a group of possible origins and excludes some other possibilities of sapphire origins. Within the group of possible origins we may come to a definite source, as long as the stone itself contains enough further evidence pointing towards its origin. It may, for example, exhibit a distinctive absorption curve or spectrum never seen in stones from other localities. At the same time it may show included crystals (identified by an electron beam instrument, which are found only that specific source. These inclusions would, therefore, exclude all other source possibilities.
Origin determination done by the SSEF are not dependent upon a single characteristics only, but are based on at least three independent diagnostic features. Our possibilities are restricted if:
- the properties found in an individual stone may also be found in stones from several localities.
- the stone is found to be free from diagnostic features.
- the possible tests which can be performed is reduced, as, for example, in mounted stones.
- the knowledge base on the type of stone being tested is not broad enough.
Sometimes gemstone deposits and mining areas cross geographic borders, such as the corundum deposits in Kenya/Tanzania and Thailand/Cambodia. In many cases, a producing country may contain different deposits which also vary from one another in the characteristics of the stones produced, such as the corundum deposits in Sri Lanka and Montana (USA).
Many persons in the gem trade have far too little knowledge of the actual range of material coming from particular sources. Even within a single mine, the stones can vary in size, color, transparency and therefore, quality, considerably. This fact must be kept in mind when associating a certain stone with a particular group. It is certainly not the overall appearance visible to the naked eye or with a hand lens which decides the origin of a stone. A possible origin is, on the contrary, proved only by a most careful investigation of all the properties and characteristics carried out by an experienced gemologist using modern scientific equipment. And if there is any doubt or ambiguity, an independent and serious scientist would not issue the report. I would appreciate it very much if the current and future customers of SSEF would understand and accept this policy, especially in cases where our result does not conform with your expectations. In some cases we cannot issue a certificate of origin; in others it turns out differently than what you expected.
I hope to have illustrated by this contribution the possibilities, techniques and the philosophy which governs our work at SSEF, regarding both colored gem reports and, as a supplement, the indications of origin.
We are currently using two different types of phrases when we issue an origin report at SSEF. If the stone shows commonly known and widely accepted diagnostic features, leading us to be very certain of the origin, we make the following statement on the report:
According to your request for an indication of origin, we confirm that the ruby described in the gemstone report mentioned above, shows inclusions as well as physical and chemical properties which, based on present gemological knowledge, are characteristic of a ruby from Burma.
In cases where the stone contains, among commonly accepted characteristic features, those recently observed and certified in our laboratory but not yet published, we use the following expression:
According to your request for an indication of origin, we confirm that the sapphire described in the gemstone report mentioned above, shows inclusions as well as physical and chemical properties, which, in our opinion, are characteristic of a sapphire from Kashmir.
I add to this letter a couple of document copies related with origin determination from SSEF. These contain all cases, including treated stones. I hope they are useful for your work. But again I want to stress that it is the trade who wants us to do these origin determinations. Personally I would prefer to omit origin designations, since they do not prove a certain quality or color of a stone. On the other hand, the buyer should be responsible for what he is spending his money on. He should take care by himself and provide his own basic knowledge, not depending only on the merchant’s or seller’s opinion.
Definition: Origin = geographical place where a gemstone is situated.
This is either the primary deposit in the parent rock or a secondary deposit where the gemstones have been accumulated after decomposition of the parent rock. Since the term Burma, Pailin and Kashmir have a geographical meaning, they should not be used to express a gemstone color type, because it is common knowledge that a particular deposit may produce different shades of colors, some of which may be found in other deposits, as well.
The need for certification of a gemstone’s origin seems to be limited to only a few species or varieties of gems, and to a small group of quite famous deposits. In certain cases, a cut stone can express its place of origin through its physical and chemical properties and by its inclusions and growth structure, as long as these are clearly distinguishable from all other types. Thus these properties must be unique, either alone or in combination. The greater the number of individual and characteristic properties found in a particular stone, the more reliable is the determination of origin. Valuable characteristics should not only positively testify to a certain origin, but the same time excludes other origin possibilities.
Because of the above, experts involved in origin determination must be aware not only of the properties and characteristics of gems from famous sources, but of the properties and characteristics of all other similar sources. Only the exclusive features, those which are unique to a particular deposit can be called diagnostic properties.
Depending on the complexity of the formation of the gem crystals and on the geologic environment, the type and number of characteristics can be quite varied. Formation of gems requires some indispensable main conditions without which the gem cannot grow, as well as side conditions which can influence the growth but are not essential to the growth. Some of these main and minor conditions which can influence the properties and characteristics of gems include:
- availability of the main constituent chemical elements, and the growth speed.
- the types of available trace elements, and their concentrations.
- transport processes and the transport media involved.
- the type of energy source involved in formation (intrusive pegmatite, metamorphic, etc.)
- pressure from free oxygen.
- cooling rate after formation.
- deformation history of the parent rock and the growing crystal.
- protogenetic inclusions, reflecting the parent rock.
- syngenetic inclusions, reflecting the transport medium and genetic formation type.
All of these factors can influence the individual characteristics of a gemstone crystal, resulting in differences in:
- the size and shape of crystals, and their growth zoning.
- color, color homogeneity, color variations.
- trace element mixture (including invisible trace elements).
- solid inclusions and twinning.
- the state of healed fissures (i.e. fingerprints), geometry and degree of restoration.
- nature of fillings in negative crystal voids.
- composition of fluid inclusions.
What sort of diagnostic origin information can we collect from a cut gemstone?
Characteristic features:
- Microscopic investigation
Color and growth zoning relative to the crystallographic structure, color inhomogeneity, twinning type (s), internal strain, observation of type and distribution of solid and fluid/gas inclusions, type of healing fissures.
- Physical and optical properties
Specific gravity, refractive indices, double refraction (birefringence), fluorescent behavior, absorption spectroscopy (UV, VIS, IR), spin resonance spectroscopy, composition of fluids and minimum temperature/pressure estimation (heat/freezing stage microscope).
- Chemical determination
Trace element determination by energy dispersive x-ray fluorescence analysis (EDS-XFA), amount or relative ratio of trace elements present (e.g. Ti, Fe, Cr, V, Ga, etc.), chemical analysis of inclusions by electron beam instruments (scanning electron microscope, electron microprobe).
Some of the observed and collected characteristics are not restricted to a certain deposit, but in combination may be of diagnostic value. Those observations which are unique for a special deposit are the most important diagnostic features in regard to origin determination. Successful origin determination involves the following steps:
Observation → Comparison → Interpretation
↑ ↑ ↑
Scrutiny Comprehension Prudence
How can we get reliable basic knowledge about materials of definite known origin?
The most simple answer to this question is to collect samples directly at the mine or source. In many cases, though, this is not possible, since the source may be exhausted, or located in an inaccessible location. Therefore we must collect our reference material from a safe source, like a museum, an old collection, etc. Information on gemstone sources can also be obtained from books and publications. Many historical gemstone sources are discussed in reference books. Geographical maps give specific information on the type of deposit, scientific publications reveal the properties of the respective material, chemical analyses of the gemstones and their inclusions are published. All observations must be in agreement with the known facts, e.g. trace elements with spectroscopic analyses, inclusions with geology, etc.
From all this information we gain a very complex view of a gemstone deposit and its production. The more material we investigate, the more dense our network becomes. We are even able to add new observations to the earlier information, building upon it. Sharing and discussing new information with knowledgeable colleagues in the same field provides an added check to our results. But it is still important to revise and recheck the fundamentals of the science by basic research and study of the literature for information on new sources and new techniques. Stagnation is dangerous.
Limitations in the determination of origin
As I have pointed out at the beginning, we use differences in properties as a means of discrimination. Properties which are repeated in stones from more than one source are not valued as diagnostic characteristics, but can nevertheless be helpful in excluding other localities which do not possess these properties. As an example, a certain shade of blue does not prove a certain origin, nor does a misty turbidity. But the misty turbidity in combination with the absence of rutile needles points towards a group of possible origins and excludes some other possibilities of sapphire origins. Within the group of possible origins we may come to a definite source, as long as the stone itself contains enough further evidence pointing towards its origin. It may, for example, exhibit a distinctive absorption curve or spectrum never seen in stones from other localities. At the same time it may show included crystals (identified by an electron beam instrument, which are found only that specific source. These inclusions would, therefore, exclude all other source possibilities.
Origin determination done by the SSEF are not dependent upon a single characteristics only, but are based on at least three independent diagnostic features. Our possibilities are restricted if:
- the properties found in an individual stone may also be found in stones from several localities.
- the stone is found to be free from diagnostic features.
- the possible tests which can be performed is reduced, as, for example, in mounted stones.
- the knowledge base on the type of stone being tested is not broad enough.
Sometimes gemstone deposits and mining areas cross geographic borders, such as the corundum deposits in Kenya/Tanzania and Thailand/Cambodia. In many cases, a producing country may contain different deposits which also vary from one another in the characteristics of the stones produced, such as the corundum deposits in Sri Lanka and Montana (USA).
Many persons in the gem trade have far too little knowledge of the actual range of material coming from particular sources. Even within a single mine, the stones can vary in size, color, transparency and therefore, quality, considerably. This fact must be kept in mind when associating a certain stone with a particular group. It is certainly not the overall appearance visible to the naked eye or with a hand lens which decides the origin of a stone. A possible origin is, on the contrary, proved only by a most careful investigation of all the properties and characteristics carried out by an experienced gemologist using modern scientific equipment. And if there is any doubt or ambiguity, an independent and serious scientist would not issue the report. I would appreciate it very much if the current and future customers of SSEF would understand and accept this policy, especially in cases where our result does not conform with your expectations. In some cases we cannot issue a certificate of origin; in others it turns out differently than what you expected.
I hope to have illustrated by this contribution the possibilities, techniques and the philosophy which governs our work at SSEF, regarding both colored gem reports and, as a supplement, the indications of origin.
We are currently using two different types of phrases when we issue an origin report at SSEF. If the stone shows commonly known and widely accepted diagnostic features, leading us to be very certain of the origin, we make the following statement on the report:
According to your request for an indication of origin, we confirm that the ruby described in the gemstone report mentioned above, shows inclusions as well as physical and chemical properties which, based on present gemological knowledge, are characteristic of a ruby from Burma.
In cases where the stone contains, among commonly accepted characteristic features, those recently observed and certified in our laboratory but not yet published, we use the following expression:
According to your request for an indication of origin, we confirm that the sapphire described in the gemstone report mentioned above, shows inclusions as well as physical and chemical properties, which, in our opinion, are characteristic of a sapphire from Kashmir.
I add to this letter a couple of document copies related with origin determination from SSEF. These contain all cases, including treated stones. I hope they are useful for your work. But again I want to stress that it is the trade who wants us to do these origin determinations. Personally I would prefer to omit origin designations, since they do not prove a certain quality or color of a stone. On the other hand, the buyer should be responsible for what he is spending his money on. He should take care by himself and provide his own basic knowledge, not depending only on the merchant’s or seller’s opinion.
Thursday, May 10, 2007
Reliability Of Origin Determination For Gemstones
(via Gemological Digest, Vol.3, No.1, 1990) Dr Henry A Hanni writes:
Definition: Origin = geographical place where a gemstone is situated.
This is either the primary deposit in the parent rock or a secondary deposit where the gemstones have been accumulated after decomposition of the parent rock. Since the term Burma, Pailin and Kashmir have a geographical meaning, they should not be used to express a gemstone color type, because it is common knowledge that a particular deposit may produce different shades of colors, some of which may be found in other deposits, as well.
The need for certification of a gemstone’s origin seems to be limited to only a few species or varieties of gems, and to a small group of quite famous deposits. In certain cases, a cut stone can express its place of origin through its physical and chemical properties and by its inclusions and growth structure, as long as these are clearly distinguishable from all other types. Thus these properties must be unique, either alone or in combination. The greater the number of individual and characteristic properties found in a particular stone, the more reliable is the determination of origin. Valuable characteristics should not only positively testify to a certain origin, but the same time excludes other origin possibilities.
Because of the above, experts involved in origin determination must be aware not only of the properties and characteristics of gems from famous sources, but of the properties and characteristics of all other similar sources. Only the exclusive features, those which are unique to a particular deposit can be called diagnostic properties.
Depending on the complexity of the formation of the gem crystals and on the geologic environment, the type and number of characteristics can be quite varied. Formation of gems requires some indispensable main conditions without which the gem cannot grow, as well as side conditions which can influence the growth but are not essential to the growth. Some of these main and minor conditions which can influence the properties and characteristics of gems include:
- availability of the main constituent chemical elements, and the growth speed.
- the types of available trace elements, and their concentrations.
- transport processes and the transport media involved.
- the type of energy source involved in formation (intrusive pegmatite, metamorphic, etc.)
- pressure from free oxygen.
- cooling rate after formation.
- deformation history of the parent rock and the growing crystal.
- protogenetic inclusions, reflecting the parent rock.
- syngenetic inclusions, reflecting the transport medium and genetic formation type.
All of these factors can influence the individual characteristics of a gemstone crystal, resulting in differences in:
- the size and shape of crystals, and their growth zoning.
- color, color homogeneity, color variations.
- trace element mixture (including invisible trace elements).
- solid inclusions and twinning.
- the state of healed fissures (i.e. fingerprints), geometry and degree of restoration.
- nature of fillings in negative crystal voids.
- composition of fluid inclusions.
What sort of diagnostic origin information can we collect from a cut gemstone?
Characteristic features:
- Microscopic investigation
Color and growth zoning relative to the crystallographic structure, color inhomogeneity, twinning type (s), internal strain, observation of type and distribution of solid and fluid/gas inclusions, type of healing fissures.
- Physical and optical properties
Specific gravity, refractive indices, double refraction (birefringence), fluorescent behavior, absorption spectroscopy (UV, VIS, IR), spin resonance spectroscopy, composition of fluids and minimum temperature/pressure estimation (heat/freezing stage microscope).
- Chemical determination
Trace element determination by energy dispersive x-ray fluorescence analysis (EDS-XFA), amount or relative ratio of trace elements present (e.g. Ti, Fe, Cr, V, Ga, etc.), chemical analysis of inclusions by electron beam instruments (scanning electron microscope, electron microprobe).
Some of the observed and collected characteristics are not restricted to a certain deposit, but in combination may be of diagnostic value. Those observations which are unique for a special deposit are the most important diagnostic features in regard to origin determination. Successful origin determination involves the following steps:
Observation → Comparison → Interpretation
↑ ↑ ↑
Scrutiny Comprehension Prudence
How can we get reliable basic knowledge about materials of definite known origin?
The most simple answer to this question is to collect samples directly at the mine or source. In many cases, though, this is not possible, since the source may be exhausted, or located in an inaccessible location. Therefore we must collect our reference material from a safe source, like a museum, an old collection, etc. Information on gemstone sources can also be obtained from books and publications. Many historical gemstone sources are discussed in reference books. Geographical maps give specific information on the type of deposit, scientific publications reveal the properties of the respective material, chemical analyses of the gemstones and their inclusions are published. All observations must be in agreement with the known facts, e.g. trace elements with spectroscopic analyses, inclusions with geology, etc.
From all this information we gain a very complex view of a gemstone deposit and its production. The more material we investigate, the more dense our network becomes. We are even able to add new observations to the earlier information, building upon it. Sharing and discussing new information with knowledgeable colleagues in the same field provides an added check to our results. But it is still important to revise and recheck the fundamentals of the science by basic research and study of the literature for information on new sources and new techniques. Stagnation is dangerous.
Limitations in the determination of origin
As I have pointed out at the beginning, we use differences in properties as a means of discrimination. Properties which are repeated in stones from more than one source are not valued as diagnostic characteristics, but can nevertheless be helpful in excluding other localities which do not possess these properties. As an example, a certain shade of blue does not prove a certain origin, nor does a misty turbidity. But the misty turbidity in combination with the absence of rutile needles points towards a group of possible origins and excludes some other possibilities of sapphire origins. Within the group of possible origins we may come to a definite source, as long as the stone itself contains enough further evidence pointing towards its origin. It may, for example, exhibit a distinctive absorption curve or spectrum never seen in stones from other localities. At the same time it may show included crystals (identified by an electron beam instrument, which are found only that specific source. These inclusions would, therefore, exclude all other source possibilities.
Origin determination done by the SSEF are not dependent upon a single characteristics only, but are based on at least three independent diagnostic features. Our possibilities are restricted if:
- the properties found in an individual stone may also be found in stones from several localities.
- the stone is found to be free from diagnostic features.
- the possible tests which can be performed is reduced, as, for example, in mounted stones.
- the knowledge base on the type of stone being tested is not broad enough.
Sometimes gemstone deposits and mining areas cross geographic borders, such as the corundum deposits in Kenya/Tanzania and Thailand/Cambodia. In many cases, a producing country may contain different deposits which also vary from one another in the characteristics of the stones produced, such as the corundum deposits in Sri Lanka and Montana (USA).
Many persons in the gem trade have far too little knowledge of the actual range of material coming from particular sources. Even within a single mine, the stones can vary in size, color, transparency and therefore, quality, considerably. This fact must be kept in mind when associating a certain stone with a particular group. It is certainly not the overall appearance visible to the naked eye or with a hand lens which decides the origin of a stone. A possible origin is, on the contrary, proved only by a most careful investigation of all the properties and characteristics carried out by an experienced gemologist using modern scientific equipment. And if there is any doubt or ambiguity, an independent and serious scientist would not issue the report. I would appreciate it very much if the current and future customers of SSEF would understand and accept this policy, especially in cases where our result does not conform with your expectations. In some cases we cannot issue a certificate of origin; in others it turns out differently than what you expected.
I hope to have illustrated by this contribution the possibilities, techniques and the philosophy which governs our work at SSEF, regarding both colored gem reports and, as a supplement, the indications of origin.
We are currently using two different types of phrases when we issue an origin report at SSEF. If the stone shows commonly known and widely accepted diagnostic features, leading us to be very certain of the origin, we make the following statement on the report:
According to your request for an indication of origin, we confirm that the ruby described in the gemstone report mentioned above, shows inclusions as well as physical and chemical properties which, based on present gemological knowledge, are characteristic of a ruby from Burma.
In cases where the stone contains, among commonly accepted characteristic features, those recently observed and certified in our laboratory but not yet published, we use the following expression:
According to your request for an indication of origin, we confirm that the sapphire described in the gemstone report mentioned above, shows inclusions as well as physical and chemical properties, which, in our opinion, are characteristic of a sapphire from Kashmir.
I add to this letter a couple of document copies related with origin determination from SSEF. These contain all cases, including treated stones. I hope they are useful for your work. But again I want to stress that it is the trade who wants us to do these origin determinations. Personally I would prefer to omit origin designations, since they do not prove a certain quality or color of a stone. On the other hand, the buyer should be responsible for what he is spending his money on. He should take care by himself and provide his own basic knowledge, not depending only on the merchant’s or seller’s opinion.
Definition: Origin = geographical place where a gemstone is situated.
This is either the primary deposit in the parent rock or a secondary deposit where the gemstones have been accumulated after decomposition of the parent rock. Since the term Burma, Pailin and Kashmir have a geographical meaning, they should not be used to express a gemstone color type, because it is common knowledge that a particular deposit may produce different shades of colors, some of which may be found in other deposits, as well.
The need for certification of a gemstone’s origin seems to be limited to only a few species or varieties of gems, and to a small group of quite famous deposits. In certain cases, a cut stone can express its place of origin through its physical and chemical properties and by its inclusions and growth structure, as long as these are clearly distinguishable from all other types. Thus these properties must be unique, either alone or in combination. The greater the number of individual and characteristic properties found in a particular stone, the more reliable is the determination of origin. Valuable characteristics should not only positively testify to a certain origin, but the same time excludes other origin possibilities.
Because of the above, experts involved in origin determination must be aware not only of the properties and characteristics of gems from famous sources, but of the properties and characteristics of all other similar sources. Only the exclusive features, those which are unique to a particular deposit can be called diagnostic properties.
Depending on the complexity of the formation of the gem crystals and on the geologic environment, the type and number of characteristics can be quite varied. Formation of gems requires some indispensable main conditions without which the gem cannot grow, as well as side conditions which can influence the growth but are not essential to the growth. Some of these main and minor conditions which can influence the properties and characteristics of gems include:
- availability of the main constituent chemical elements, and the growth speed.
- the types of available trace elements, and their concentrations.
- transport processes and the transport media involved.
- the type of energy source involved in formation (intrusive pegmatite, metamorphic, etc.)
- pressure from free oxygen.
- cooling rate after formation.
- deformation history of the parent rock and the growing crystal.
- protogenetic inclusions, reflecting the parent rock.
- syngenetic inclusions, reflecting the transport medium and genetic formation type.
All of these factors can influence the individual characteristics of a gemstone crystal, resulting in differences in:
- the size and shape of crystals, and their growth zoning.
- color, color homogeneity, color variations.
- trace element mixture (including invisible trace elements).
- solid inclusions and twinning.
- the state of healed fissures (i.e. fingerprints), geometry and degree of restoration.
- nature of fillings in negative crystal voids.
- composition of fluid inclusions.
What sort of diagnostic origin information can we collect from a cut gemstone?
Characteristic features:
- Microscopic investigation
Color and growth zoning relative to the crystallographic structure, color inhomogeneity, twinning type (s), internal strain, observation of type and distribution of solid and fluid/gas inclusions, type of healing fissures.
- Physical and optical properties
Specific gravity, refractive indices, double refraction (birefringence), fluorescent behavior, absorption spectroscopy (UV, VIS, IR), spin resonance spectroscopy, composition of fluids and minimum temperature/pressure estimation (heat/freezing stage microscope).
- Chemical determination
Trace element determination by energy dispersive x-ray fluorescence analysis (EDS-XFA), amount or relative ratio of trace elements present (e.g. Ti, Fe, Cr, V, Ga, etc.), chemical analysis of inclusions by electron beam instruments (scanning electron microscope, electron microprobe).
Some of the observed and collected characteristics are not restricted to a certain deposit, but in combination may be of diagnostic value. Those observations which are unique for a special deposit are the most important diagnostic features in regard to origin determination. Successful origin determination involves the following steps:
Observation → Comparison → Interpretation
↑ ↑ ↑
Scrutiny Comprehension Prudence
How can we get reliable basic knowledge about materials of definite known origin?
The most simple answer to this question is to collect samples directly at the mine or source. In many cases, though, this is not possible, since the source may be exhausted, or located in an inaccessible location. Therefore we must collect our reference material from a safe source, like a museum, an old collection, etc. Information on gemstone sources can also be obtained from books and publications. Many historical gemstone sources are discussed in reference books. Geographical maps give specific information on the type of deposit, scientific publications reveal the properties of the respective material, chemical analyses of the gemstones and their inclusions are published. All observations must be in agreement with the known facts, e.g. trace elements with spectroscopic analyses, inclusions with geology, etc.
From all this information we gain a very complex view of a gemstone deposit and its production. The more material we investigate, the more dense our network becomes. We are even able to add new observations to the earlier information, building upon it. Sharing and discussing new information with knowledgeable colleagues in the same field provides an added check to our results. But it is still important to revise and recheck the fundamentals of the science by basic research and study of the literature for information on new sources and new techniques. Stagnation is dangerous.
Limitations in the determination of origin
As I have pointed out at the beginning, we use differences in properties as a means of discrimination. Properties which are repeated in stones from more than one source are not valued as diagnostic characteristics, but can nevertheless be helpful in excluding other localities which do not possess these properties. As an example, a certain shade of blue does not prove a certain origin, nor does a misty turbidity. But the misty turbidity in combination with the absence of rutile needles points towards a group of possible origins and excludes some other possibilities of sapphire origins. Within the group of possible origins we may come to a definite source, as long as the stone itself contains enough further evidence pointing towards its origin. It may, for example, exhibit a distinctive absorption curve or spectrum never seen in stones from other localities. At the same time it may show included crystals (identified by an electron beam instrument, which are found only that specific source. These inclusions would, therefore, exclude all other source possibilities.
Origin determination done by the SSEF are not dependent upon a single characteristics only, but are based on at least three independent diagnostic features. Our possibilities are restricted if:
- the properties found in an individual stone may also be found in stones from several localities.
- the stone is found to be free from diagnostic features.
- the possible tests which can be performed is reduced, as, for example, in mounted stones.
- the knowledge base on the type of stone being tested is not broad enough.
Sometimes gemstone deposits and mining areas cross geographic borders, such as the corundum deposits in Kenya/Tanzania and Thailand/Cambodia. In many cases, a producing country may contain different deposits which also vary from one another in the characteristics of the stones produced, such as the corundum deposits in Sri Lanka and Montana (USA).
Many persons in the gem trade have far too little knowledge of the actual range of material coming from particular sources. Even within a single mine, the stones can vary in size, color, transparency and therefore, quality, considerably. This fact must be kept in mind when associating a certain stone with a particular group. It is certainly not the overall appearance visible to the naked eye or with a hand lens which decides the origin of a stone. A possible origin is, on the contrary, proved only by a most careful investigation of all the properties and characteristics carried out by an experienced gemologist using modern scientific equipment. And if there is any doubt or ambiguity, an independent and serious scientist would not issue the report. I would appreciate it very much if the current and future customers of SSEF would understand and accept this policy, especially in cases where our result does not conform with your expectations. In some cases we cannot issue a certificate of origin; in others it turns out differently than what you expected.
I hope to have illustrated by this contribution the possibilities, techniques and the philosophy which governs our work at SSEF, regarding both colored gem reports and, as a supplement, the indications of origin.
We are currently using two different types of phrases when we issue an origin report at SSEF. If the stone shows commonly known and widely accepted diagnostic features, leading us to be very certain of the origin, we make the following statement on the report:
According to your request for an indication of origin, we confirm that the ruby described in the gemstone report mentioned above, shows inclusions as well as physical and chemical properties which, based on present gemological knowledge, are characteristic of a ruby from Burma.
In cases where the stone contains, among commonly accepted characteristic features, those recently observed and certified in our laboratory but not yet published, we use the following expression:
According to your request for an indication of origin, we confirm that the sapphire described in the gemstone report mentioned above, shows inclusions as well as physical and chemical properties, which, in our opinion, are characteristic of a sapphire from Kashmir.
I add to this letter a couple of document copies related with origin determination from SSEF. These contain all cases, including treated stones. I hope they are useful for your work. But again I want to stress that it is the trade who wants us to do these origin determinations. Personally I would prefer to omit origin designations, since they do not prove a certain quality or color of a stone. On the other hand, the buyer should be responsible for what he is spending his money on. He should take care by himself and provide his own basic knowledge, not depending only on the merchant’s or seller’s opinion.
Monday, April 30, 2007
Origin Determination Of Rubies, Sapphires And Emeralds
The lecture was delivered on the 8th December, 2004 at AIGS by Dietmar Schwarz and Christian Dunaigre, Gubelin Gem Lab, Switzerland.
In brief:
Historical data: The concept of country of origin determination started 60+ years ago in Switzerland by Dr. Eduard Gubelin who did methodical studies on internal features of gemstones originating from important gem localities around the world. During 1950s and 1970s the number of important gem deposits were restricted due to political and economic reasons. Some of the major deposits include:
Ruby: Ratnapura/Elahera in Sri Lanka
Mogok Stone Tract / Mong Hshu / Namya in Burma
Trat province in Thailand
Magari / Umba valley in East Africa
Different localities in Vietnam
Different localities in Madagascar
Sapphires: Ratnapura / Elahera in Sri Lanka
Mogok Stone Tract in Burma
Kanchanaburi / Chantaburi in Thailand
Different localities in Australia
Different localities in Madagascar
Different localities in the USA
Emeralds: Muzo / Chivor in Colombia
Different localities in Zambia
Sandawana in Zimbabwe
Ural mountains in Russia
Different localities in Brazil
Different localities in Afghanistan
Different localities in Pakistan
In today’s gem market, traders like to submit a ruby, sapphire or emerald for origin determination due to its high value. Inclusions do affect prices. There are number of reasons why inclusions alone are unreliable for determining the origin of gemstones. The current gemological knowledge of inclusions for various ruby + sapphire + emerald + other important colored stone occurrences are incomplete. Study of inclusions is a relatively new science and there is so much that remains to be learned + so many inclusions that have yet to be identified and catalogued. The key areas to be studied are:
- variation of the inclusion parameters within samples from a given locality
- similarity of inclusion populations in samples from different localities
- what sort of diagnostic origin information can we collect from a cut gemstone
- limitations in the determination of origin
- chemical fingerprinting
- advanced instruments such as UV, VIS-NIR, FTIR, Raman +++
During the 80s and 90s many new gem deposits were discovered. It was found that the mineralogical-gemological properties of the new sources were quite similar or even identical to those observed from the traditional sources. For instance blue sapphires from Madagascar displayed features that resembled sapphires from Sri Lanka, East Africa, Burma or even Kashmir. At the same time gemstones even when found in similar geological environments still showed some locality-specific features which allowed a clear separation from gems originating from a deposit of the same generic type such rubies from the Mogok and Mong Hshu.
Today gemological laboratories dealing with origin determination of colored stones are confronted with the gem production of an increasing number of mining areas all over the world. Some of the traditional sources are not producing gems consistently. Without any doubt the island of Madagascar has enormous potential for almost all gemstone species located in different regions of the country and related to different types of host rocks. Advanced + proprietary treatment techniques in rubies, sapphires and emerald may result in the elimination of characteristic features and make origin determination more difficult.
In brief:
Historical data: The concept of country of origin determination started 60+ years ago in Switzerland by Dr. Eduard Gubelin who did methodical studies on internal features of gemstones originating from important gem localities around the world. During 1950s and 1970s the number of important gem deposits were restricted due to political and economic reasons. Some of the major deposits include:
Ruby: Ratnapura/Elahera in Sri Lanka
Mogok Stone Tract / Mong Hshu / Namya in Burma
Trat province in Thailand
Magari / Umba valley in East Africa
Different localities in Vietnam
Different localities in Madagascar
Sapphires: Ratnapura / Elahera in Sri Lanka
Mogok Stone Tract in Burma
Kanchanaburi / Chantaburi in Thailand
Different localities in Australia
Different localities in Madagascar
Different localities in the USA
Emeralds: Muzo / Chivor in Colombia
Different localities in Zambia
Sandawana in Zimbabwe
Ural mountains in Russia
Different localities in Brazil
Different localities in Afghanistan
Different localities in Pakistan
In today’s gem market, traders like to submit a ruby, sapphire or emerald for origin determination due to its high value. Inclusions do affect prices. There are number of reasons why inclusions alone are unreliable for determining the origin of gemstones. The current gemological knowledge of inclusions for various ruby + sapphire + emerald + other important colored stone occurrences are incomplete. Study of inclusions is a relatively new science and there is so much that remains to be learned + so many inclusions that have yet to be identified and catalogued. The key areas to be studied are:
- variation of the inclusion parameters within samples from a given locality
- similarity of inclusion populations in samples from different localities
- what sort of diagnostic origin information can we collect from a cut gemstone
- limitations in the determination of origin
- chemical fingerprinting
- advanced instruments such as UV, VIS-NIR, FTIR, Raman +++
During the 80s and 90s many new gem deposits were discovered. It was found that the mineralogical-gemological properties of the new sources were quite similar or even identical to those observed from the traditional sources. For instance blue sapphires from Madagascar displayed features that resembled sapphires from Sri Lanka, East Africa, Burma or even Kashmir. At the same time gemstones even when found in similar geological environments still showed some locality-specific features which allowed a clear separation from gems originating from a deposit of the same generic type such rubies from the Mogok and Mong Hshu.
Today gemological laboratories dealing with origin determination of colored stones are confronted with the gem production of an increasing number of mining areas all over the world. Some of the traditional sources are not producing gems consistently. Without any doubt the island of Madagascar has enormous potential for almost all gemstone species located in different regions of the country and related to different types of host rocks. Advanced + proprietary treatment techniques in rubies, sapphires and emerald may result in the elimination of characteristic features and make origin determination more difficult.
Saturday, December 02, 2006
Geographic Origin on Emerald Identification Reports
GIA writes:
The Gemological Institute of America (GIA) begins offering geographic origin determinations on its Emerald Identification Reports effective December 1, 2006.
Shane McClure, director of Gem Identification in GIA's California Laboratory, said the service expansion is a pivotal step for GIA. "The Institute has always held that the intrinsic quality of an emerald was the most important factor in determining its market value."
"While we staunchly believe that the quality of gem material will always be of primary importance, we recognize that the marketplace perceives the country of origin of an emerald to be of added value, and is therefore a factor in its valuation," said McClure.
More info @ www.gia.edu
The Gemological Institute of America (GIA) begins offering geographic origin determinations on its Emerald Identification Reports effective December 1, 2006.
Shane McClure, director of Gem Identification in GIA's California Laboratory, said the service expansion is a pivotal step for GIA. "The Institute has always held that the intrinsic quality of an emerald was the most important factor in determining its market value."
"While we staunchly believe that the quality of gem material will always be of primary importance, we recognize that the marketplace perceives the country of origin of an emerald to be of added value, and is therefore a factor in its valuation," said McClure.
More info @ www.gia.edu
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