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, corundum, Tanzania.12, spinel, tanzanite, zoisite, Merelani, Mahenge, Tunduru

In a parcel of over thirty rubies from Myanmar’s Mong Hsu mines, all of the stones contained zoned clouds of cottony ‘silk’, believed to be diaspore, as seen in the sample shown in Figure 1. However, this stone stood out from the rest of the lot. In addition to the wispy diaspore silk, it also contained several bands of fine, intact silk needles, likely rutile (Figure 2). It was, in fact, the only stone in this suite to contain this type of silk. While rutile silk needles are uncommon in Mong Hsu rubies, they have been reported on rare occasions, and we have also observed them in a few samples from our laboratory’s reference collection. It is worth noting that despite the intact silk needles, this stone was determined to have been heated. Supporting evidence included other inclusions, such as melted fingerprints, as well as a clear 3309 series with 3232 in the infrared spectrum and zoned chalky short-wave ultraviolet fluorescence. This serves as an important reminder that the presence of intact silk needles does not always indicate that a stone is unheated.

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, spinel, synthetic spinel, spinel treatments, heat treatment, spinel diffusion, nickel diffusion

Describes an unusual inclusion in garnet.

gems, corundum, Burma.12, treatments.6, Mogok, ruby, heat treatment, inclusions.5

Detection of heat treatment below 1200°C in ruby and sapphire can present challenges to gemologists, as alterations to the material are often subtle. In this study, the authors heated Burmese ruby samples from Mogok, Myanmar, at temperatures ranging from 600° to 1500°C. The samples were documented using macrophotography, photomicrography of inclusions, ultraviolet fluorescence imaging, and spectroscopic analysis (Raman, ultraviolet/visible/near-infrared, and infrared) to record any changes, with a focus on features that could help detect heat treatment. A wide variety of solid inclusions, including calcite, mica, spinel, and zircon, were found in Mogok ruby. Many of those were found to be sensitive to heat treatment with regard to morphology and phase transition; their reactions varied depending on a number of factors such as size, distance from the surface, and species. Microscopic examination provided useful visual indications of heat treatment, even at lower temperatures. Raman analysis of calcite and spinel inclusions also proved valuable in providing complementary evidence of low-temperature heat treatment.

gems, spinel, inclusions

gems, corundum, inclusions.5, Sri Lanka.12

One of the beauties of working with gemstones is that each time you peer into a stone, you get a glimpse of the universe held within. When we first examined the scene in a star sapphire (see above), we were delighted with the view. A feature that immediately stands out is the triangular crystal, which displays terraced growth features and iridescence on the surface when illuminated with a fiber-optic light. Analysis with micro Raman revealed that this crystal is apatite. What makes the scene even more stunning is the way the crystal seems to float over a cloud of rutile silk. This same silk is what creates asterism in the stone. While in this case the apatite crystal resides in a sapphire from Sri Lanka, apatite has also been reported in corundum from a variety of sources, including Afghanistan, Cambodia, Madagascar, Myanmar, Nigeria, Pakistan, Tanzania, Thailand, the United States, and Vietnam. Apatite can be found not only in ruby and sapphire from different origins, but also in many other types of gems. In our laboratory, we have encountered apatite inclusions in emerald, spinel, and garnet. Apatite is a relatively common mineral, so it is not surprising to find it so often as an inclusion. Although it may occur frequently, in this instance it is anything but mundane.

gems, gemology, ruby, sapphire, jade, inclusions.5, corundum, garnet, quartz, China, Tibet, Thailand, Burma, Myanmar, Sri Lanka, Inner Mongolia, India, Madagascar, Mozambique, Tanzania, Rwanda, East Africa, Greenland

From the dawn of time, precious stones have both attracted and fascinated humans in ways that few other items could. For while objects of desire are found throughout the natural world, physical beauty is too often ephemeral. From the allure of a man, woman, flower or butterfly, through the fleeting moments of a sunset, there is little that lasts and practically nothing that can be passed down to our descendants. The exception is precious stones. Not only are they the most durable creations of Mother Nature, but their visual splendor is truly eternal. This book presents a completely fresh approach to the subject. Dubbing it humanistic gemology, the authors take readers around the world, showing the places they have explored in their search for gems, along with the people and cultures encountered along the way. Within this volume, remarkable photographs of the human world are interwoven with images of the microscopic realm of the gems themselves. In a lifetime beset by time control, where living is broken into ever smaller bits, as you browse through these pages suddenly you plunge into a domain of frozen time, one that affords vistas of millions or even billions of years. For jewels offer not just superficial beauty, but a window on the primordial forces that birthed both our planet and universe. Inside Out – Gemology Through Lotus-Colored Glasses represents a fascinating new direction for gemology, linking the external and internal worlds of precious stones for the first time.

gems, corundum, inclusions.5, Mozambique.12, ruby, böhmite

Gemologists at Bangkok’s Lotus Gemology laboratory recently examined a large lot of rubies believed to originate from the Montepuez area of Mozambique. Microscopic examination confirmed that assessment. Many of these stones displayed features in their infrared spectra that are typical for böhmite, with a characteristic “twin peak” spectrum at ~3309 and 3089 cm⁻¹. One of the stones showed a large area cut through on a pavilion facet that appeared to be a foreign substance. A similar substance was seen in many of the fissures in the stone. Judicious use of the hot point under the microscope produced no reaction. We then moved to analyze the substance via micro-Raman. The result was böhmite, which neatly confirmed the results from the infrared spectrum. Böhmite, AlO(OH), is a polymorph of diaspore. In corundum it is generally a secondary mineral, infilling surface-reaching openings after the host corundum has grown.