Polished Prices writes:
The South African government moved ahead this week with several key appointments to its state diamond regulatory body.
Among the appointments for the new regulator - in charge of licencing, the Kimberley Process and beneficiation - is Louis Selekane, current CEO of the South African Diamond Board, who will become chief executive.
Martin Mononela, previously chief director at the Department of Minerals and Energy, will act as general manager. According to Mononela, the boards of the State Diamond Trader as well as the regulator – each comprising of 16 civil and industry representatives – have already been appointed.
Based on the new South African Diamond legislation, 10% by value of the country’s diamond production must be made available to the State Diamond Trader. The government is currently in the process of appointing a State Trader, whose activities will be overseen but its own independent board of directors.
Licence holders applying for goods from the State Diamond Trader are required to polish and cut 80% of their supplies in South Africa. The remaining 20% is exempted from export duty, said Mononela.
“After personnel have been put in place at the trading body, the trading will begin," said Mononela, adding this could be as early as August 2007. “In terms of the law, the negotiations have been finalised with the producers,” he said.
The President is expected to promulgate the new legislation no later than August 2007.
More info @ http://www.polishedprices.com/article.shtml?ID=1000004502
Thursday, July 12, 2007
A Diamond District Far From 47th Street
Hilary Larson writes about Brugges and Antwerp + its international status as the center for diamonds and fashion + other viewpoints @ http://www.thejewishweek.com/news/newscontent.php3?artid=14252
Precious Stones Of The Future From The Laboratory
An insider (s) view + tips for students studying synthetic gemstone identification course (s).
(via The Journal of Gemmology, Vol.XVI, No.7, July 1979)
A report on M. Pierre Gilson’s talk
On the 11th October, 1978, a talk was given to members of the Association by M Pierre Gilson on ‘Precious Stones of the Future from the Laboratory’ in the Geological Museum Cinema Theatre, South Kensington. The theatre was full when the proceedings were opened and the speaker was introduced by the vice-chairman, Dr David Callaghan, FGA, who said M Gilson produced the very best that man could produce and was able to do in a relatively short time things which Nature took very much longer to achieve; his talent and the vast range of materials that he was producing were quite fantastic.
M Gilson’s talk then took the form of a running commentary no the hundred or so slides which he showed during the evening and he left few people in doubt about the progress made in the last fifty or sixty years. He reminded the audience that Verneuil was the first to make synthetic ruby and sapphire at the beginning of the century: with his relatively simple method he was able to produce a boule in one of several colors in a matter of three hours or so, and his synthetic corundum was soon used to make the jewels in watches.
In contrast, M Gilson’s company takes as long as nine months to grow synthetic emeralds. They start with a seed—synthetic material of the highest quality—and grow it as a non-stop process for nine months. A continuous supply of electricity is essential, because it is important to allow crystallization to take place at a constant temperature if good crystals are to be grown. Accordingly arrangements have been made to ensure that the company is guaranteed a supply of electricity privately in case there should be a failure in the public supply due to breakdown or perhaps a strike.
But it is not just a matter of having the right equipment and know how: experimentation also is necessary. Before success in making synthetic turquoise was achieved, thirty different phosphates had to be crystallized.
The equipment now used in the Gilson laboratories is very sophisticated and quite advanced. In order to study the size and formation of the tiny ‘beads’ which make up such gemstones as emeralds an electron microscope is used. A spectrophotometer is another essential piece of equipment, because it is important to be able to control absorption to within one part per million.
With synthetic emeralds M Gilson has found it beneficial to cut at a specific angle in relation to the seed crystal on which the new material has been grown. He used slides to explain that the main difference between synthetic and natural emerald lies in the nature of the inclusions. In the synthetic material the ‘veil’ is twisted, whereas in the natural stone it is straight. He added that Nature produced only one good emerald for every million crystals formed: in the laboratory it was essential to have a very much higher success rate. Emerald production in the Gilson laboratory takes precisely nine months, since, if you wait any longer, crystallization may have stopped. A simple—but impractical! –test to distinguish between natural and synthetic emerald was mentioned: if you heat it to one thousand degrees and it turns white when it cools, you know it is natural. He added that the hardness of emerald was affected by the extent of inclusions in a given stone.
Opal was next discussed. Opal is pure silica: it acts like a prism and the colors which can be seen are pure spectral colors. Gilson synthetic opals contain more pure colors than natural material because they contain more pure constituents. Laboratory production of opal calls for a very high temperature: natural opal is no longer being created because temperatures are not high enough. Even in the laboratory it is impossible to produce two identical opals. Production starts with the production of millions of tiny beads, each about 0.3 microns in diameter, and these eventually form the finished material. M Gilson’s most recent improvements involve the removal of all traces of water from synthetic opals, and this gets rid of cracks and helps to avoid some of the hazards associated with the natural material. With natural opals, it is interesting to note that material found at depth of more than six meters is often noticeably better than stones found near the surface.
Natural turquoise contains iron, and in some cases customers are disappointed when the iron turns green after a year or two. ‘Our own stones are pure turquoise, so this problem doesn’t arise’—but a process has now been developed so that iron can be introduced to the surface of synthetic turquoise.
With lapis, although pyrites (its inclusions) can be synthesized, M Gilson uses natural pyrites. ‘Each day nine hundred tons of natural pyrites are mined: I cannot compete with that!’ He is now successfully synthesizing coral and used calcite which is now being mined in France.
In answer to a question whether he could suggest any methods of testing stones to tell the difference between real and synthetic specimens, he said: ‘We work on developing new scientific products, but when it comes to identification you are the experts.’ Asked whether it was his intention to produce stones so similar to the natural product that they could not be detected, he replied: ‘We are not competing with Nature but merely trying to improve on it by producing more pure stones—more beautiful ones for the jeweler to work with.’
Mr Alec Farn asked if M Gilson had produced any emeralds without chromium but with the addition of vanadium, and M Gilson replied that he had not—and even if it was done, could the result be described as emerald?’ ‘If people want chromium in emerald, then why shouldn’t we give it to them?’
Offering a tip for improving opals, M Gilson said that if soaked over night in ethyl alcohol all moisture in the stone would be driven out and the color improved—but it was essential not to do this if the stone was a triplet! And in reply to an enquiry whether he had carried out any experiment on the jadeite family, he smiled and said: ‘Yes, we are working on this problem.’
When asked how long he had been trying to make synthetic stones before he had his first success, he said he took fifteen years to succeed with emerald, ten years with opal, and eight years with turquoise: and because of slow reactions and the length of time it took to grow a single crystal before it was known whether or not the experiment was a success, research was becoming more difficult and expensive. Some members of the audience were surprised when M Gilson mentioned that his main business was not the production of synthetic gemstones but the manufacture of about nine tons of ceramics each month for industrial use.
(via The Journal of Gemmology, Vol.XVI, No.7, July 1979)
A report on M. Pierre Gilson’s talk
On the 11th October, 1978, a talk was given to members of the Association by M Pierre Gilson on ‘Precious Stones of the Future from the Laboratory’ in the Geological Museum Cinema Theatre, South Kensington. The theatre was full when the proceedings were opened and the speaker was introduced by the vice-chairman, Dr David Callaghan, FGA, who said M Gilson produced the very best that man could produce and was able to do in a relatively short time things which Nature took very much longer to achieve; his talent and the vast range of materials that he was producing were quite fantastic.
M Gilson’s talk then took the form of a running commentary no the hundred or so slides which he showed during the evening and he left few people in doubt about the progress made in the last fifty or sixty years. He reminded the audience that Verneuil was the first to make synthetic ruby and sapphire at the beginning of the century: with his relatively simple method he was able to produce a boule in one of several colors in a matter of three hours or so, and his synthetic corundum was soon used to make the jewels in watches.
In contrast, M Gilson’s company takes as long as nine months to grow synthetic emeralds. They start with a seed—synthetic material of the highest quality—and grow it as a non-stop process for nine months. A continuous supply of electricity is essential, because it is important to allow crystallization to take place at a constant temperature if good crystals are to be grown. Accordingly arrangements have been made to ensure that the company is guaranteed a supply of electricity privately in case there should be a failure in the public supply due to breakdown or perhaps a strike.
But it is not just a matter of having the right equipment and know how: experimentation also is necessary. Before success in making synthetic turquoise was achieved, thirty different phosphates had to be crystallized.
The equipment now used in the Gilson laboratories is very sophisticated and quite advanced. In order to study the size and formation of the tiny ‘beads’ which make up such gemstones as emeralds an electron microscope is used. A spectrophotometer is another essential piece of equipment, because it is important to be able to control absorption to within one part per million.
With synthetic emeralds M Gilson has found it beneficial to cut at a specific angle in relation to the seed crystal on which the new material has been grown. He used slides to explain that the main difference between synthetic and natural emerald lies in the nature of the inclusions. In the synthetic material the ‘veil’ is twisted, whereas in the natural stone it is straight. He added that Nature produced only one good emerald for every million crystals formed: in the laboratory it was essential to have a very much higher success rate. Emerald production in the Gilson laboratory takes precisely nine months, since, if you wait any longer, crystallization may have stopped. A simple—but impractical! –test to distinguish between natural and synthetic emerald was mentioned: if you heat it to one thousand degrees and it turns white when it cools, you know it is natural. He added that the hardness of emerald was affected by the extent of inclusions in a given stone.
Opal was next discussed. Opal is pure silica: it acts like a prism and the colors which can be seen are pure spectral colors. Gilson synthetic opals contain more pure colors than natural material because they contain more pure constituents. Laboratory production of opal calls for a very high temperature: natural opal is no longer being created because temperatures are not high enough. Even in the laboratory it is impossible to produce two identical opals. Production starts with the production of millions of tiny beads, each about 0.3 microns in diameter, and these eventually form the finished material. M Gilson’s most recent improvements involve the removal of all traces of water from synthetic opals, and this gets rid of cracks and helps to avoid some of the hazards associated with the natural material. With natural opals, it is interesting to note that material found at depth of more than six meters is often noticeably better than stones found near the surface.
Natural turquoise contains iron, and in some cases customers are disappointed when the iron turns green after a year or two. ‘Our own stones are pure turquoise, so this problem doesn’t arise’—but a process has now been developed so that iron can be introduced to the surface of synthetic turquoise.
With lapis, although pyrites (its inclusions) can be synthesized, M Gilson uses natural pyrites. ‘Each day nine hundred tons of natural pyrites are mined: I cannot compete with that!’ He is now successfully synthesizing coral and used calcite which is now being mined in France.
In answer to a question whether he could suggest any methods of testing stones to tell the difference between real and synthetic specimens, he said: ‘We work on developing new scientific products, but when it comes to identification you are the experts.’ Asked whether it was his intention to produce stones so similar to the natural product that they could not be detected, he replied: ‘We are not competing with Nature but merely trying to improve on it by producing more pure stones—more beautiful ones for the jeweler to work with.’
Mr Alec Farn asked if M Gilson had produced any emeralds without chromium but with the addition of vanadium, and M Gilson replied that he had not—and even if it was done, could the result be described as emerald?’ ‘If people want chromium in emerald, then why shouldn’t we give it to them?’
Offering a tip for improving opals, M Gilson said that if soaked over night in ethyl alcohol all moisture in the stone would be driven out and the color improved—but it was essential not to do this if the stone was a triplet! And in reply to an enquiry whether he had carried out any experiment on the jadeite family, he smiled and said: ‘Yes, we are working on this problem.’
When asked how long he had been trying to make synthetic stones before he had his first success, he said he took fifteen years to succeed with emerald, ten years with opal, and eight years with turquoise: and because of slow reactions and the length of time it took to grow a single crystal before it was known whether or not the experiment was a success, research was becoming more difficult and expensive. Some members of the audience were surprised when M Gilson mentioned that his main business was not the production of synthetic gemstones but the manufacture of about nine tons of ceramics each month for industrial use.
Chrysocolla
Chemistry: Hydrous copper silicate (variable).
Crystal system: Monoclinic; cryptocrystalline massive.
Color: Semi-translucent to opaque; green to blue; chrysocolla quartz; chrysocolla opal; Eilat stone: mixture of chrysocolla, turquoise, malachite and other copper minerals.
Hardness: 2 - 4
Cleavage: None; Fracture: even.
Specific gravity: 2.0 – 2.4; Eilat stone: 2.8 – 3.2
Refractive index: 1.50 approx; Eilat stone: 1.46 – 1.57 (varies with composition)
Luster: Vitreous.
Dispersion: -
Dichroism: -
Occurrence: Zone of weathering in copper lodes and deposits; Chile, DR Congo; Russia, USA, Peru, Australia.
Notes
Porous; R.I and heavy liquids can damage; may impregnate quartz/opal; color may be ‘mountain green, bluish green, sky blue, turquoise blue, often with an opal/enamel-like texture; Eilat stone found near Eilat, Gulf of Aquaba in Red Sea; mottled blue and green; contain copper carbonate malachite; reacts vigorously with acids; cut mainly cabochons.
Crystal system: Monoclinic; cryptocrystalline massive.
Color: Semi-translucent to opaque; green to blue; chrysocolla quartz; chrysocolla opal; Eilat stone: mixture of chrysocolla, turquoise, malachite and other copper minerals.
Hardness: 2 - 4
Cleavage: None; Fracture: even.
Specific gravity: 2.0 – 2.4; Eilat stone: 2.8 – 3.2
Refractive index: 1.50 approx; Eilat stone: 1.46 – 1.57 (varies with composition)
Luster: Vitreous.
Dispersion: -
Dichroism: -
Occurrence: Zone of weathering in copper lodes and deposits; Chile, DR Congo; Russia, USA, Peru, Australia.
Notes
Porous; R.I and heavy liquids can damage; may impregnate quartz/opal; color may be ‘mountain green, bluish green, sky blue, turquoise blue, often with an opal/enamel-like texture; Eilat stone found near Eilat, Gulf of Aquaba in Red Sea; mottled blue and green; contain copper carbonate malachite; reacts vigorously with acids; cut mainly cabochons.
Wednesday, July 11, 2007
Sightholders Losses May Ignite A Banking Revolt
Chaim Even-Zohar writes about sightholder concerns + the credit business + other viewpoints @ http://www.idexonline.com/portal_FullEditorial.asp?TextSearch=&KeyMatch=0&id=26181
Examination Of Maxixe-type Blue And Green Beryl
Only a very few know about Maxixe-type beryl (s), and often they are confused for aquamarine, iolite or even quartz. I have seen gem dealers getting puzzled when they have to deal with lots, and eventually they are sold as something else. You don't want to make god-like statement (s) when you don't have comparison stones or at times you go through 'momentary autism'--you just go blank/inert. Only a sophisticated lab with experienced staff will be able to recognize the tell-tale signs. Many labs do not have sample (s) of Maxixe-type beryl (s) for comparsion purposes so they get confused and misidentify them. At times it's like two blind walking the street (s).
(via The Journal of Gemmology, Vol.13, No.8, October 1973) K Nassau / D L Wood writes:
Abstract
Blue Maxixe beryl, kept in the dark since 1917, and current blue and green beryl showing similar characteristics have been examined b absorption spectroscopy, gamma ray spectroscopy, chemical analysis, and light, heat and irradiation treatments. All three show an anomalous dichroism (the ordinary ray is more blue than the extraordinary ray, while in aquamarine the reverse is true) and an unusual narrow band spectrum in the red and yellow regions. In all three cases the color is bleached by exposure to daylight or on heating and can be recovered by neutron or gamma ray irradiation. A color center not involving a transition metal such as Fe, Co, Cu, etc. is indicated. Examination of 23 faceted ‘sapphire’ blue beryl gemstones by gamma ray spectroscopy indicates that three had definitely been colored by neutron irradiation; the others may or may not have been treated by irradiation.
Introduction
About 1917 blue beryl was found in the Maxixe mine in Minas Gerais, Brazil, which had the following unusual properties: it showed a strong anomalous dichroism, a narrow band absorption spectrum for the ordinary ray which produces a pronounced ‘sapphire’ or ‘cobalt’ blue (distinctly different from the blue of aquamarine beryl); and the color faded on exposure to light. These and other properties were reported in 1933 and 1935. We consider any beryl to be ‘Maxixe-type’ beryl if it shows these three unusual properties: dichroism with blue in the ordinary ray; narrow-banded absorptions in the ordinary ray spectrum; and bleaching on exposure to light or heat. Some recent material of this type has become available, and our attention was drawn to the unusual absorption spectrum by Mr R Crowningshield.
Experimental
We have examined in detail the following: a piece of the original Maxixe find that has been kept from extended exposure to light since 1917, courtesy of Mr B W Anderson; 23 specimens of currently commercially available deep blue faceted stones (ranging from four to ten carats in weight) as well as blue rough, from an unspecified locality said to be in Brazil; and three dark green stones and some dark green rough, possibly from the same current locality. All exhibit the three properties just mentioned. Although there were some minor differences, all these specimens showed pronounced blue/colorless, blue/pale pink, or green/yellow dichroism with a similar characteristic w spectrum in the 5000 to 7500 Angstrom region.
Permission was obtained to expose to light four current deep blue stones, current deep blue and green rough, and part of the old Maxixe rough (either to daylight with intermittent sun or to a 100-watt frosted tungsten light bulb at a distance of six inches in an air-conditioned room) After one week all had faded significantly, ending with only about half of the original color or less. The bleaching was then completed by heating to a maximum of 235º (450ºF) for 30 minutes, resulting in a yellow or pale pink color. By comparison, aquamarine is customarily heated to a much higher temperature (400ºC - 750ºF) to improve the color, which remains stable to light.
Examination of all the specimens by gamma-ray spectroscopy using a lithium drifted germanium detector indicated in three of the faceted stones the presence of a small amount of Caesium-134, a radioactive species with a half life of 2 years. This is absent in nature, but produced by neutron irradiation of natural Caesium-133 in the specimens. These stones must therefore have been treated by neutron irradiation. The other specimens did not show this behavior and have probably not been irradiated with neutrons. On heating one of the partially bleached cut stones to 150ºC for 30 minutes there was no significant further change in color. However, after 30 minutes at 200ºC (about 400ºF) only a very pale pink color remained. Neutron irradiation (15 minutes at 10¹³ neutrons/cm²/sec) now returned the stone to a blue color even deeper than its original color. Another similar stone (blue/pale pink dichroism), when heated by Mr R Crowningshield, bleached completely to pale pink in less than 30 minutes at 95ºC (200ºF). This stone was exposed to gamma rays (2 x 107 rads from Cobalt 60) and also turned deep blue. This gamma ray irradiation does not leave any evidence of treatment, producing the usual characteristic w spectrum. As expected from the case of heat bleaching, this stone also bleached very rapidly in light (significantly in only 15 hours).
The green material, when bleached to a deep yellow by sunlight, could be returned to green by neutron irradiation, to a weak blue/green by X-rays, but was hardly changed by gamma rays from Cobalt-60. The recolored material (both blue and green) could be bleached again by light. The green could also be changed to yellow by a 30-minute heat treatment at 150ºC, while heating to 400ºC removed the yellow color as was previously noted in an ordinary yellow beryl; neutron irradiation returned this colorless material to green.
Analysis showed a high iron content in the green material (about 0.2%), but essentially none in the old Maxixe sample (0.000X%). This is consistent with the spectral evidence that the deep yellow component is due to Fe3+ in the octahedral Al site and indicates that Fe is not involved in the narrow banded w spectrum. Other transition metals such as Co, Cu, etc. are essentially absent. Since the blue material can be bleached by exposure to light or quite low temperatures and recovered by irradiation, a color center not involving a transition metal ion is indicated. The minor differences in the spectra may well be associated with differences in the total alkali content, the old Maxixe being high (about 2%), the green low (less than 0.1%).
Neutron irradiation was also tried on several of the beryl specimens used in our previous study. One of these, a colorless beryl showed a faint blue color after irradiation, and on examination showed a weak w spectrum of the Maxixe-type. Accordingly it appears that not any beryl can be irradiated to give a Maxixe-type color, but neither does it appear to be necessary to have material from a unique location. Investigation on this point is continuing.
Conclusions
There is some variation in spectrum, iron content, alkali content, color, and rate of bleaching by either light or heat. Nevertheless, in contrast to the many ordinary varieties of beryl known over the centuries, these specimens show sufficient similarity to merit a common designation, and we have used the term ‘Maxixe-type’ based on the first reported occurrence. At present there is not enough information to decide if this type of material originates from one or several localities. It appears that the color of some of this material may be as originally found, although some material has definitely been neutron irradiated either to form the color, to improve the color, or to return color which has been bleached by exposure to light or to heat. Some or all of the rest may have been colored by gamma rays.
Based on the observations here reported we believe that any blue or green beryl (particularly if the blue color is of ‘sapphire’ type) showing anomalous dichroism with the blue color in the ordinary ray and sharp absorption bands for the ordinary ray in the 5000 to 7500 Angstrom region should be designated as ‘Maxixe-type’. Such a beryl will face, either on exposure to light or on heating. Such a beryl may or may not have been irradiated with neutrons or with gamma rays. It is in fact not possible to determine whether a given stone has been treated or how fast it will fade.
In the words of Mr Crowningshield ‘potential buyers should be alerted to the possibility that any stone of this type, which they consider, may fade too rapidly to be a satisfactory jewelry stone.’
Appendix
A note on color centers
Most of the color in gems and minerals is caused by unpaired electrons in major ingredients such as the copper in malachite and turquoise, or in impurities such as the chromium in ruby and emerald or the iron in aquamarine and citrine. Alternatively there is color caused by physical structure, as in opal and labradorite (the optical diffraction grating effect).
But in some materials, where there is no such color causing ingredient or physical structure present, it is possible for ‘color centers’ to cause a variety of colors. Color centers have been studied intensively, but only few have been understood. Frequently this involves a vacancy (omitted atom) or some other type of defect (sometimes an impurity) which can hold (but does not of itself possess) an unpaired electron.
Examples of color centers occur in halite or sylvite (made purple to black by various treatments), fluorite (green, purple, etc.) and smoky quartz. A frequent characteristic of color centers is that exposure to light or to relatively low temperatures may permit the unpaired electrons to pair off, thus removing the color. Irradiation by X-rays, neutrons, or some other form of penetrating radiation may cause the color to return by unpairing the electrons again. An unusual, only partly understood color center is involved in the amethyst form of quartz which also contains iron as an impurity. Amethyst is turned yellow or green by heat, and can be recolored with X-ray irradiation. However not just any quartz colored green or yellow with iron will go to amethyst with irradiation—some specific defect must still be associated with the iron impurity. Synthetic quartz containing iron must be grown in one specific direction to produce this specific color center and enable amethyst to be produced on subsequent X-ray irradiation. The color of amethyst is unusually stable for a color center, although it will fade over a period of many years or in hours at 400 to 600ºC. The relative ease with which the color is produced by X-rays is consistent with this stability to light and to heat.
In the case of the deep blue beryl there does not seem to be any specific impurity present. It is likely therefore that a vacancy is involved which can hold an unpaired electron. The relative ease of fading implies that the electrons pair off readily, and the difficulty of returning the color is consistent with this instability.
(via The Journal of Gemmology, Vol.13, No.8, October 1973) K Nassau / D L Wood writes:
Abstract
Blue Maxixe beryl, kept in the dark since 1917, and current blue and green beryl showing similar characteristics have been examined b absorption spectroscopy, gamma ray spectroscopy, chemical analysis, and light, heat and irradiation treatments. All three show an anomalous dichroism (the ordinary ray is more blue than the extraordinary ray, while in aquamarine the reverse is true) and an unusual narrow band spectrum in the red and yellow regions. In all three cases the color is bleached by exposure to daylight or on heating and can be recovered by neutron or gamma ray irradiation. A color center not involving a transition metal such as Fe, Co, Cu, etc. is indicated. Examination of 23 faceted ‘sapphire’ blue beryl gemstones by gamma ray spectroscopy indicates that three had definitely been colored by neutron irradiation; the others may or may not have been treated by irradiation.
Introduction
About 1917 blue beryl was found in the Maxixe mine in Minas Gerais, Brazil, which had the following unusual properties: it showed a strong anomalous dichroism, a narrow band absorption spectrum for the ordinary ray which produces a pronounced ‘sapphire’ or ‘cobalt’ blue (distinctly different from the blue of aquamarine beryl); and the color faded on exposure to light. These and other properties were reported in 1933 and 1935. We consider any beryl to be ‘Maxixe-type’ beryl if it shows these three unusual properties: dichroism with blue in the ordinary ray; narrow-banded absorptions in the ordinary ray spectrum; and bleaching on exposure to light or heat. Some recent material of this type has become available, and our attention was drawn to the unusual absorption spectrum by Mr R Crowningshield.
Experimental
We have examined in detail the following: a piece of the original Maxixe find that has been kept from extended exposure to light since 1917, courtesy of Mr B W Anderson; 23 specimens of currently commercially available deep blue faceted stones (ranging from four to ten carats in weight) as well as blue rough, from an unspecified locality said to be in Brazil; and three dark green stones and some dark green rough, possibly from the same current locality. All exhibit the three properties just mentioned. Although there were some minor differences, all these specimens showed pronounced blue/colorless, blue/pale pink, or green/yellow dichroism with a similar characteristic w spectrum in the 5000 to 7500 Angstrom region.
Permission was obtained to expose to light four current deep blue stones, current deep blue and green rough, and part of the old Maxixe rough (either to daylight with intermittent sun or to a 100-watt frosted tungsten light bulb at a distance of six inches in an air-conditioned room) After one week all had faded significantly, ending with only about half of the original color or less. The bleaching was then completed by heating to a maximum of 235º (450ºF) for 30 minutes, resulting in a yellow or pale pink color. By comparison, aquamarine is customarily heated to a much higher temperature (400ºC - 750ºF) to improve the color, which remains stable to light.
Examination of all the specimens by gamma-ray spectroscopy using a lithium drifted germanium detector indicated in three of the faceted stones the presence of a small amount of Caesium-134, a radioactive species with a half life of 2 years. This is absent in nature, but produced by neutron irradiation of natural Caesium-133 in the specimens. These stones must therefore have been treated by neutron irradiation. The other specimens did not show this behavior and have probably not been irradiated with neutrons. On heating one of the partially bleached cut stones to 150ºC for 30 minutes there was no significant further change in color. However, after 30 minutes at 200ºC (about 400ºF) only a very pale pink color remained. Neutron irradiation (15 minutes at 10¹³ neutrons/cm²/sec) now returned the stone to a blue color even deeper than its original color. Another similar stone (blue/pale pink dichroism), when heated by Mr R Crowningshield, bleached completely to pale pink in less than 30 minutes at 95ºC (200ºF). This stone was exposed to gamma rays (2 x 107 rads from Cobalt 60) and also turned deep blue. This gamma ray irradiation does not leave any evidence of treatment, producing the usual characteristic w spectrum. As expected from the case of heat bleaching, this stone also bleached very rapidly in light (significantly in only 15 hours).
The green material, when bleached to a deep yellow by sunlight, could be returned to green by neutron irradiation, to a weak blue/green by X-rays, but was hardly changed by gamma rays from Cobalt-60. The recolored material (both blue and green) could be bleached again by light. The green could also be changed to yellow by a 30-minute heat treatment at 150ºC, while heating to 400ºC removed the yellow color as was previously noted in an ordinary yellow beryl; neutron irradiation returned this colorless material to green.
Analysis showed a high iron content in the green material (about 0.2%), but essentially none in the old Maxixe sample (0.000X%). This is consistent with the spectral evidence that the deep yellow component is due to Fe3+ in the octahedral Al site and indicates that Fe is not involved in the narrow banded w spectrum. Other transition metals such as Co, Cu, etc. are essentially absent. Since the blue material can be bleached by exposure to light or quite low temperatures and recovered by irradiation, a color center not involving a transition metal ion is indicated. The minor differences in the spectra may well be associated with differences in the total alkali content, the old Maxixe being high (about 2%), the green low (less than 0.1%).
Neutron irradiation was also tried on several of the beryl specimens used in our previous study. One of these, a colorless beryl showed a faint blue color after irradiation, and on examination showed a weak w spectrum of the Maxixe-type. Accordingly it appears that not any beryl can be irradiated to give a Maxixe-type color, but neither does it appear to be necessary to have material from a unique location. Investigation on this point is continuing.
Conclusions
There is some variation in spectrum, iron content, alkali content, color, and rate of bleaching by either light or heat. Nevertheless, in contrast to the many ordinary varieties of beryl known over the centuries, these specimens show sufficient similarity to merit a common designation, and we have used the term ‘Maxixe-type’ based on the first reported occurrence. At present there is not enough information to decide if this type of material originates from one or several localities. It appears that the color of some of this material may be as originally found, although some material has definitely been neutron irradiated either to form the color, to improve the color, or to return color which has been bleached by exposure to light or to heat. Some or all of the rest may have been colored by gamma rays.
Based on the observations here reported we believe that any blue or green beryl (particularly if the blue color is of ‘sapphire’ type) showing anomalous dichroism with the blue color in the ordinary ray and sharp absorption bands for the ordinary ray in the 5000 to 7500 Angstrom region should be designated as ‘Maxixe-type’. Such a beryl will face, either on exposure to light or on heating. Such a beryl may or may not have been irradiated with neutrons or with gamma rays. It is in fact not possible to determine whether a given stone has been treated or how fast it will fade.
In the words of Mr Crowningshield ‘potential buyers should be alerted to the possibility that any stone of this type, which they consider, may fade too rapidly to be a satisfactory jewelry stone.’
Appendix
A note on color centers
Most of the color in gems and minerals is caused by unpaired electrons in major ingredients such as the copper in malachite and turquoise, or in impurities such as the chromium in ruby and emerald or the iron in aquamarine and citrine. Alternatively there is color caused by physical structure, as in opal and labradorite (the optical diffraction grating effect).
But in some materials, where there is no such color causing ingredient or physical structure present, it is possible for ‘color centers’ to cause a variety of colors. Color centers have been studied intensively, but only few have been understood. Frequently this involves a vacancy (omitted atom) or some other type of defect (sometimes an impurity) which can hold (but does not of itself possess) an unpaired electron.
Examples of color centers occur in halite or sylvite (made purple to black by various treatments), fluorite (green, purple, etc.) and smoky quartz. A frequent characteristic of color centers is that exposure to light or to relatively low temperatures may permit the unpaired electrons to pair off, thus removing the color. Irradiation by X-rays, neutrons, or some other form of penetrating radiation may cause the color to return by unpairing the electrons again. An unusual, only partly understood color center is involved in the amethyst form of quartz which also contains iron as an impurity. Amethyst is turned yellow or green by heat, and can be recolored with X-ray irradiation. However not just any quartz colored green or yellow with iron will go to amethyst with irradiation—some specific defect must still be associated with the iron impurity. Synthetic quartz containing iron must be grown in one specific direction to produce this specific color center and enable amethyst to be produced on subsequent X-ray irradiation. The color of amethyst is unusually stable for a color center, although it will fade over a period of many years or in hours at 400 to 600ºC. The relative ease with which the color is produced by X-rays is consistent with this stability to light and to heat.
In the case of the deep blue beryl there does not seem to be any specific impurity present. It is likely therefore that a vacancy is involved which can hold an unpaired electron. The relative ease of fading implies that the electrons pair off readily, and the difficulty of returning the color is consistent with this instability.
Charoite
Chemistry: Calcium potassium silicate with hydroxyl and fluorite.
Crystal system: Rock; massive.
Color: Semi-translucent to opaque; various shades of purple (Mn and / or Fe); may be solid color, banded, streaky purple and white, or fibrous (possibly containing black, gray or brownish orange areas).
Hardness: 5 - 6
Cleavage: None; Fracture: splintery to granular.
Specific gravity: 2.68
Refractive index: 1.55 (mean).
Luster: Vitreous, if well polished.
Dispersion: -
Dichroism: -
Occurrence: Siberia (Russia), NW of Alden.
Notes
Decorative ornamental material (distinctive structure); discovered in 1976 along the Charo River, northeast of Lake Baikal; purplish rock may contain radiating greenish black needles of Agirine augite (a pyroxene); yellowish to orangy prismatic crystals (Tipaskite); whitish green patches of microcline feldspar and other minerals; flouorescence: inert but feldspar may glow dull red; beads, carvings.
Crystal system: Rock; massive.
Color: Semi-translucent to opaque; various shades of purple (Mn and / or Fe); may be solid color, banded, streaky purple and white, or fibrous (possibly containing black, gray or brownish orange areas).
Hardness: 5 - 6
Cleavage: None; Fracture: splintery to granular.
Specific gravity: 2.68
Refractive index: 1.55 (mean).
Luster: Vitreous, if well polished.
Dispersion: -
Dichroism: -
Occurrence: Siberia (Russia), NW of Alden.
Notes
Decorative ornamental material (distinctive structure); discovered in 1976 along the Charo River, northeast of Lake Baikal; purplish rock may contain radiating greenish black needles of Agirine augite (a pyroxene); yellowish to orangy prismatic crystals (Tipaskite); whitish green patches of microcline feldspar and other minerals; flouorescence: inert but feldspar may glow dull red; beads, carvings.
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