gems, corundum, Australia.12, Cambodia.12, China.12, Thailand.12, Nigeria.12, inclusions.5, treatments.6, basalt, sapphire

Basalt-related blue sapphires typically have an oversaturated blue color causing the stones to be too dark when faceted. Low-temperature heat treatment can lighten dark material. However, it is difficult to identify this treatment using standard gemological testing and microscopic examination. For instance, unheated sapphires are transported to the earth’s surface by hot, basaltic magma which may have thermally altered their inclusions, causing them to look similar to those seen in artificially heated material. In this study, 50 basalt-related blue sapphires were heat treated in air (oxidizing atmosphere). Changes in color appearance, UV fluorescence, internal features, and spectroscopic properties post treatment were compared with the results before treatment to find suitable approaches for detecting heat treatment on blue sapphires from basalt-related deposits. The main factors affecting the sapphires’ response to heat treatment include the temperatures employed and the duration of the treatment process. Initial experiments at temperatures of 500–1500 °C for 7 hours showed that the blue color appears to lighten at 700 °C and higher. Temperatures ranging from 700 to 1050 °C were then selected for a more in-depth study on the effect of heating time with durations of 1.75, 7, and 28 hours. The results showed negligible change to a slight lightening of the blue color after treatment at 700 °C, while an obvious lightening of the blue color occurred at 900 and 1050 °C. Some mineral inclusions, iron stains, and partially healed fractures showed signs of alteration during these heating experiments, while needles and minute particles did not show any signs of change. All unheated samples studied were inert to short-wave ultraviolet radiation. After heating, most remained inert under short-wave UV, but a few samples exhibited a very weak chalky green fluorescence. FTIR spectra obtained from the samples varied considerably, with differences in peak intensities before and after heating. Differences were also seen as the duration of heating was changed. In most cases, unheated blue sapphires from basalt-related deposits revealed the characteristic 3309 cm⁻¹ series (sharp peaks at 3309, 3232 and 3186 cm⁻¹) in the FTIR spectrum with the intensity of 3232 cm⁻¹ being much lower than that of 3309 cm⁻¹. After heating at 700 °C and 900 °C, the intensity of the 3309 cm⁻¹ peak decreased and the 3232 cm⁻¹ peak increased, respectively. However, in most cases, some samples that initially showed a relatively intense 3232 cm⁻¹ peak before treatment exhibited a more intense 3309 cm⁻¹ peak and a less intense 3232 cm⁻¹ peak post treatment. After heating at 1050 °C for 1.75 hours, we recorded a decrease in the intensity of the 3309 cm⁻¹ peak and an increase in the 3232 cm⁻¹ peak, to the point where they were of almost comparable intensity. When subsequently heated for 7 and 28 hours, the intensity of the 3309 cm⁻¹ peak increased and that of the 3232 cm⁻¹ peak decreased. UV-Vis-NIR spectra obtained from the samples heated at 900 °C and 1050 °C for 1.75, 7, and 28 hours showed a reduction in the height/intensity of the broad band centered at 580 nm related to an Fe²⁺–Ti⁴⁺ intervalence charge transfer. This reduction is the root cause of the lighter color after heat treatment. The results of this study showed that even with advanced testing, it is very challenging to separate basalt-related sapphires that have been artificially heated from natural unheated stones, owing to the variable results associated with the experimental temperatures and durations used. Inclusion studies may provide sufficient evidence in some cases, but even when comparing the inclusions seen before and after treatment, separation often remains challenging.

gems, color science, color theory, art, anthropology, Rome, ancient color terms, Greece, Greek poetry

Deciphering colour terms from early Greek poetry (that is, from poetry prior to the fifth century) is one of Classical philology’s longest-standing conundrums. What should a modern reader make of Homer’s “wine-dark” (οἶνοψ) cattle or his “violet” (ἰοειδής) sea? How is it that only a select few of the hues from Newton’s seven-colour ROYGBIV spectrum are represented in early Greek poetry? Through its ongoing assessment and comparison of languages from all over the world representing a wide variety of cultures, cultural linguistics offers a means of addressing these difficult questions. In its earlier stages, however, scholars in this sub-field of anthropology turned to the work of Classical philologists on Greek colour terms, using Homeric Greek in particular as one of their comparanda. This chapter does not attempt to answer the thorny questions posed above, which are likely to inspire a great deal of scholarship for years to come, but rather will trace the beginnings of colour term study by both philologists and anthropologists. If it is true that, as Turner claims, “anthropology presents perhaps the most tangled case of philological influence on a humanistic discipline,” then the history of the study of colour terms provides a clear narrative of how the roots of these disciplines grew entangled with each other. I relate this story beginning with nineteenth-century work on Homer which linked colour terminology to the ancient Greeks’ visual capabilities and situating it in the context of the scientific work of Sir Isaac Newton on colour, John Dalton on colour-blindness, and Charles Darwin on evolution. I then take up the origins of cultural linguistics, tracing how this process parallels the development of anthropology itself, before moving on to the work of early twentieth-century philologists on colour. In the final section of this chapter, I return to mid-century cultural linguistics, specifically Brent Berlin and Paul Kay’s inclusion of Homeric Greek in their seminal Basic Color Terms in 1969. I address why this dialect of ancient Greek has had such influence in the history of the study of colour terms and how varying trends in cultural linguistics have affected its use by both anthropologists and classicists. Much like classical studies, the study of colour terms is fundamentally interdisciplinary, currently requiring the participation of, according to Dedrick and Paramei, “psychophysicists and physiologists, cognitive psychologists and linguists, ethnographers and ethnoscientists, computer scientists and philosophers and neuropsychologists and ophthalmologists and literary scholars (who must) take each other seriously, on pain of mistake or irrelevance.” This chapter maps out where the work of classicists and anthropologists on colour terms has intersected and diverged to examine the enduring influence of Homeric Greek on this field of study.

gems, corundum, inclusions.5

Crystallographically oriented, linear inclusions in corundum are often referred to as “boehmite needles” or “polycrystalline boehmite” (boehmite is the orthorhombic aluminum hydroxide γ-AlOOH). These inclusions are oriented along the edges of the rhombohedral faces and form angles of about 90°. They are always found at the intersection of twin lamellae, formed by twinning along the rhombohedral faces. They contain apparently polycrystalline material tentatively identified (at least in some cases) as boehmite. These are common in natural corundum and sometimes used as a criterion to separate natural from synthetic corundum. Boehmite can be recognized through its infrared absorption. The great majority of the “needle”-containing gem corundum showed no boehmite infrared absorption, thus leading us to believe that these inclusions have a different origin. Microscopic observation reveals three aspects: some are lath- or ribbon-shaped, others are clearly negative crystals, and sometimes they appear as dotted lines. At the outcrop of the feature on the gem’s surface there is most commonly a void that can be followed into the gem, so the “needle” is essentially empty. This feature was also documented in a flux-grown synthetic ruby with no boehmite infrared signal. These channels are favored during titanium diffusion and take on color first, as diffusion is much faster in the empty space. It is known that in a small number of materials—some metals, calcite, and diamond—hollow channels may form at the intersection of twin lamellae, caused by deformation twinning. This was discovered by Gustav Rose (1868) in calcite, and thus the features are called “Rose channels” (figure 1). We believe that “boehmite needles” are in fact Rose channels. Even when very small, these channels would explain the optical relief observed, without a change in chemistry or infrared absorption. They fit the crystallographic nature of the structures observed.

gems, corundum, inclusions.5, Burma.12

This study characterizes blue sapphires from Myanmar’s Mogok Stone Tract using standard gemological observations together with spectroscopic and chemical analyses. The authors document the appearance, internal features, trace-element chemistry, and spectral characteristics of Mogok sapphires, emphasizing features useful for geographic origin determination. The material commonly shows blue color related to iron and titanium, with variations in zoning and inclusion assemblages reflecting the complex geological environment of the deposit. Microscopic features, absorption spectra, and trace-element patterns are compared with those of sapphires from other major sources to identify characteristics that may assist in separating Mogok material from stones of similar appearance. The study provides a detailed reference dataset for laboratory identification and contributes to a better understanding of the gemological characteristics and origin determination of blue sapphires from this historically important Burmese deposit.

gems, corundum, inclusions.5, photomicrography, E. Billie Hughes, Lotus Gemology

This is not the first time that gemologists rummage through the mysterious spaces of crystals and end up being so surprised by the images they produce that they ask themselves whether they have stepped into another area: the field of real art. When, after printing them, these photos become tangible objects like paintings, their question becomes clearer: is there a spontaneous form of art that doesn’t need human beings any more, revealed by the simple reproduction of innate phenomena? After all Pliny himself, a precursor of all “modern” gemological reasoning, warned scholars to consider gemstones precious just because they have the priceless value of making us contemplate the spectacular and intriguing lessons to learn from Nature. According to the great Latin naturalist, their beauty contained an explicit invitation to contemplation. An invitation for us, miserable and frail humans, to immerse and lose ourselves in them and read the wonderful design of the perfect system of the Magister Vitae, which gave order to the world.

gems, corundum, USA.12, Montana.12, sapphire, melt inclusions

We report here compositions of glassy melt inclusions hosted in sapphires (gem quality corundum) from three alluvial deposits in Montana, USA including the Rock Creek, Dry Cottonwood Creek, and Missouri River deposits. While it is likely that sapphires in these deposits were transported to the surface by Eocene age volcanic events, their ultimate origin is still controversial with many models suggesting the sapphires are xenocrysts with a metamorphic or metasomatic genesis. Melt inclusions are trachytic, dacitic, and rhyolitic in composition. Microscopic observations allow separation between primary and secondary melt inclusions. The primary melt inclusions represent the silicate liquid that was present at the time of sapphire formation and are enriched in volatile components (8–14wt.%). Secondary melt inclusions analyzed here for Dry Cottonwood Creek and Rock Creek sapphires are relatively volatile depleted and represent the magma that carried the sapphires to the surface. We propose that alluvial Montana sapphires from these deposits formed through a peritectic melting reaction during partial melting of a hydrated plagioclase-rich protolith (e.g. an anorthosite). The heat needed to drive this reaction was likely derived from the intrusion of mantle-derived mafic magmas near the base of the continental lithosphere during rollback of the Farallon slab around 50Ma. These mafic magmas may have ended up as the ultimate carrier of the sapphires to the surface as evidenced by the French Bar trachybasalt near the Missouri River deposit. Alternatively, the trachytic, rhyolitic, and dacitic secondary melt inclusions at Rock Creek and Dry Cottonwood Creek suggests that the same magmas produced during the partial melting event that generated the sapphires may have also transported them to the surface. Determining the genesis of these deposits will further our understanding of sapphire deposits around the world and may help guide future sapphire prospecting techniques. This work is also important to help reveal the history of mantle-derived mafic magmas as they pass through the continental crust.

corundum, inclusions.5, Burma.12, gems

gems, jade, jadeite, fei cui, jadeitite, Japan, fei cui, geology

This paper presents a review of Itoigawa’s jadeitite in history, culture, process of rediscovery, and geological characteristics. The people of the Jomon age used jadeitite as tools as far as 7000 years ago, making it one of the oldest jadeitite cultures in the world. The jadeitites from Itoigawa were the source of ornaments such as pendants or comma–shaped beads that can be dated to the Jomon age through to the Nara period. These ornaments are widely found in Japanese Islands from Hokkaido to Okinawa Prefecture, and also in the southern part of the Korean Peninsula. The jadeitite, however, was not used after the Nara period. The disappearance of jadeitite culture is not well understood, but it may have been caused by the introduction of Buddhism into Japan. Therefore, the existence of jadeitite in Japan was forgotten for a period of 1200 years after the Nara period. Mr. Eizo Ito rediscovered jadeitite from Itoigawa when he identified the durable green rock in the Kotakigawa River in 1938. His success was inspired by the idea of Mr. Gyofu Soma. The rediscovered jadeitite was studied by Dr. Yoshinori Kawano of the Tohoku Imperial University in 1939. There are large jadeitite boulders weighing more than 100 tons found in several areas of the Kotakigawa and Ohmigawa Rivers. These areas are designated national natural monuments. The jadeitite from Itoigawa can be found in various colors such as white, gray, black, lavender, and blue. These color variations are caused by the presence of trace elements such as iron and titanium in jadeite and omphacite, and tiny graphite inclusions in jadeitite. The absence of quartz and euhederal jadeite crystals with natrolite and veinlets of jadeitite indicates that the Itoigawa jadeitite does not form through decomposition of albite, but by hydrothermal activity. Some strontium dominant minerals such as itoigawaite were first found in jadeitite from Itoigawa. These strontium dominant minerals form in the calcium depleted hydrothermal solution in the late stages of jadeitite formation. The Jomon is the oldest jadeitite culture worldwide, and the first documented use of precious stones in the history of mankind. In addition, the jadeitite found in Itoigawa is the oldest known unit of its kind.

gems, corundum, History.1

In 2011, an extraordinary piece of gold jewelry set with precious stones was found in a woman’s tomb discovered not far from Rome and dating from the third century AD. Our examination and archaeometric analyses enabled us to identify the technique used to make the jewel and to characterize the nature and provenance of the gemstones. The analyses showed that all the stones were natural sapphires. Their inclusions and gemmological features indicate that they came from southern and south- eastern Asia, thus gaining insights about trade routes and the luxury-goods market during the Roman imperial period.

corundum, ruby, inclusions.5, synthetic corundum.7, gems