gems, spinel

The authors examined a 7.01 ct spinel reportedly from Tanzania. Under short-wave (254 nm) ultraviolet light, a small fluorescent spot was observed on the stone’s surface, caused by cut-through crystal inclusions. Micro-Raman analysis identified the inclusions as diopside, phlogopite, and edenite, forming a cluster of transparent crystals associated with a dark, opaque pyrite grain (see above, A). In reflected light, the inclusions showed luster distinct from the spinel host, with the pyrite exhibiting a golden metallic luster (see above, B). Under short-wave ultraviolet light, the crystals fluoresced in different colors: white for diopside, yellow for phlogopite, and blue for edenite (see above, C). Fluorescence from inclusions is often overlooked but can provide important identification clues.

gems, spinel, Tanzania, inclusions, diopside, phlogopite, edenite

Gemology is a forensic science, and often what we don’t know can be as interesting as what we do know. Recently, the authors encountered a fascinating spinel. The owner noted that the stone (reportedly from Myanmar, formerly Burma) contained an inclusion feature with a bubble inside. Closer inspection revealed a negative crystal or cavity that indeed contained a mobile bubble (see above). With gentle heating from the warmth of the microscope’s light bulb, the authors were able to see the bubble expand and contract.

gems, jade, pyroxene jade, fei cui, Chinese history, 1766 BC-220 AD, Chinese history, 220-960, Featherwork, tian tsui, nephrite, mineralogy, history of mineralogy, jadeite, fei cui, omphacite, kosmochlor, Fischer-Other, Broken Bangle

Broken Bangle | The Blunder-Besmirched History of Jade Nomenclature is an in-depth discussion of jade nomenclature and features works from the studios of some of China’s leading contemporary jade and stone carvers. The book takes readers through the entire tortuous history of jade nomenclature, detailing how the current monikers were based on misinformation and misunderstanding of the gems’ true natures. Thus, the Chinese gem yù (amphibole jade) was named “nephrite” by French mineralogist Alexis Damour in the mistaken belief it was the same as the Mesoamerican pyroxene jade that a 16th Century Spanish doctor himself misinterpreted as being used to treat kidney disease (‘nephritus’). Later, Damour created a mineral species he called “jadeite” for what was actually a gem rock already known in China as fei cui. But this gemological whodunit is much more than a dry recitation of jade nomenclature. It includes a detailed section on the occurrence and mineralogy of both yù (nephrite) and fei cui. Because jade is so intimately connected with Chinese culture, much of the Middle Kingdom’s fascinating history is also woven through its pages. Broken Bangle features dozens of color images of both historical documents and spectacular photos of contemporary jade and stone carving in China. For those whose mental picture of jade sculpture is a cliché Chinese goddess statue, prepare to have your minds blown.

gems, spinel, inclusions

Recently, a 3.14 ct pink spinel was submitted to the Lotus Gemology laboratory, with encouragement from the owner to examine its inclusions. When viewed under the microscope, the spinel did not disappoint. Suspended within was a richly textured, opaque metallic crystal (see above). Although attempts were made to identify the inclusion using micro-Raman spectroscopy, its identity remained inconclusive. However, based on the crystal’s appearance, it was likely a metal sulfide. Similar inclusions in spinel have been reported as pyrite (E.B. Hughes et al., “Spinel inclusions: An exercise in aesthetics,” InColor, No. 43, 2019, pp. 66–73; N. Renfro et al., “Micro-features of spinel,” Spring 2021 G&G, pp. 46–49).

gems, jade, pyroxene jade, fei cui, Chinese history, 1766 BC-220 AD, Chinese history, 220-960, Featherwork, tian tsui, nephrite, mineralogy, history of mineralogy, jadeite, fei cui, omphacite, kosmochlor, Fischer-Other, Broken Bangle

Broken Bangle | The Blunder-Besmirched History of Jade Nomenclature is an in-depth discussion of jade nomenclature and features works from the studios of some of China’s leading contemporary jade and stone carvers. The book takes readers through the entire tortuous history of jade nomenclature, detailing how the current monikers were based on misinformation and misunderstanding of the gems’ true natures. Thus, the Chinese gem yù (amphibole jade) was named “nephrite” by French mineralogist Alexis Damour in the mistaken belief it was the same as the Mesoamerican pyroxene jade that a 16th Century Spanish doctor himself misinterpreted as being used to treat kidney disease (‘nephritus’). Later, Damour created a mineral species he called “jadeite” for what was actually a gem rock already known in China as fei cui. But this gemological whodunit is much more than a dry recitation of jade nomenclature. It includes a detailed section on the occurrence and mineralogy of both yù (nephrite) and fei cui. Because jade is so intimately connected with Chinese culture, much of the Middle Kingdom’s fascinating history is also woven through its pages. Broken Bangle features dozens of color images of both historical documents and spectacular photos of contemporary jade and stone carving in China. For those whose mental picture of jade sculpture is a cliché Chinese goddess statue, prepare to have your minds blown.

gems, inclusions, hackmanite, apatite

Hackmanite, Na₈Al₆Si₆O₂₄(Cl₂,S), is a variety of sodalite notable for its tenebrescence. When kept in darkness, samples can fade to pale purple and even gray or translucent to opaque white. When exposed to long-wave ultraviolet illumination, they can display a strong orange fluorescence reaction. After exposure to sunlight or artificial light with a UV component, samples can quickly develop a much stronger color. One hackmanite sample recently examined by the author (figure 1) showed this phenomenon. Another hackmanite was submitted that displayed an interesting elongated white inclusion (figure 2, left) that was identified by micro-Raman as apatite. As we examined the sample in the microscope, we tried exposing it to a 6-watt long-wave UV light for approximately one second. Almost immediately, a change was observed. The hackmanite developed a more vibrant purple color that is clearly displayed in figure 2 (right).

gems, corundum, treatments.6, Sri Lanka.12

In recent years, one concern our laboratory has heard from clients and from other gemologists is the issue of color stability in corundum. Some sapphires, particularly those with a strong yellow component (including padparadscha sapphire), contain unstable color centers that may fade when the stone is exposed to light and/or heat (K. Nassau and G.K. Valente, “The seven types of yellow sapphire and their stability to light,” Winter 1987 G&G, pp. 222–231). We regularly test for this in the laboratory by conducting a fade test. Most of the sapphires we encounter that have an unstable color are unheated stones. Recently an orange sapphire of approximately 10 ct was submitted for testing (figure 1). Microscopic examination revealed signs of heat treatment, with partially dissolved silk, several glassy discoids (figure 2), and melted crystals (figure 3). A fade test was conducted by placing the stone approximately 5 cm under a 120-watt incandescent spotlight for at least an hour, and a dramatic difference was observed. The color had changed from orange to a vivid yellow (again, see figure 1). Under normal conditions, high-temperature heat treatment (at least 1200–1300°C) will bleach any color centers that might be present. This suggests that the orange color was activated after the heat treatment. It is possible that this occurred either by subjecting the stone to artificial irradiation or by placing it in sunlight (Nassau and Valente, 1987). However, we are unable to state definitively what process was used to activate the orange color. Several weeks later, we tested another yellow sapphire of approximately 18 ct (figure 4). In this instance, the stone’s features were consistent with those of unheated sapphire. Again, a fade test was performed with the 120-watt spotlight, which mildly warmed the stone to approximately 100°C. Its color also faded after the fade test, and the owner was informed. The owner explained that they had previously put the sapphire in direct sunlight, which would have brought the color back to what was likely its stable state, a process described by Nassau. To test this, we placed the stone in direct sunlight for 30 minutes, and the more intense yellow color did return. Unfortunately, placing the gem in direct sunlight behind a window in our office did not have the same effect. Upon seeing the color return after being placed in direct sunlight, we decided to try another fade test, this time using a light source that would not warm up the stone. An XD-300 xenon light source was used, and the stone was placed within 5 cm of a fiber-optic light guide connected to this source. After exposure to this cooler light source for over an hour, the color did not fade. This suggests that the mild heat of the 120-watt spotlight, not just the light, faded the stone’s color and that the more intense yellow color displayed after exposure to sunlight could indeed be considered the stable color. We have since adjusted our fade tests to be light-only by switching to this cooler light source to avoid the heat generated with the 120-watt spotlight. Our experience with these sapphires has been a fascinating case study in the color stability of yellow sapphire. This example reinforces the importance of considering all possibilities when testing stones in the laboratory. We do not fully understand the exact causes of these changes, and much remains to be learned.

gems, garnet, inclusions, apatite

In the micro-world, it can be challenging to identify inclusions based on sight alone, as many minerals can have a similar appearance. Occasionally, though, some inclusions have characteristic features that can aid in their identification. Recently this author had the opportunity to observe a pyrope-spessartine garnet, reportedly from Lindi Province, Tanzania, that contained blue crystal inclusions ensconced among intersecting needles (see above). Analysis with micro-Raman spectroscopy identified the inclusions as apatite. Apatites are known for their bright blue hues, and these inclusions offered an attractive example. While this sample hails from Tanzania, blue apatite has previously been reported as an inclusion in garnet from Madagascar (Winter 2020 G&G Micro-World, p. 526). These inclusions’ distinctive appearance may help gemologists recognize the material in other samples, but further analysis should be performed to identify them definitively.

gems, spinel, inclusions

gems, apatite, treated apatite