(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.
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