gems, corundum, turquoise, diamond, advanced instruments, spectroscopy

UV-Vis-NIR (Ultra Violet-Visible-Near Infrared) Spectroscopy allows to analyse the interaction between matter and electromagnetic radiation in the Ultraviolet, Visible and Near Infrared wavelength range. The spectral range of these instruments, depending on the model, can go from 200 nanometers (nm) of the C-Ultraviolet until 1100 nm of the Near Infrared and it’s quite broader than the visible region (400-700 nm) available by using the optical spectroscope. The theoretical principles, which will not been elaborated in this article, refer to the optical spectroscopy: every single material subjected to radiation reacts in a specific way by absorbing portions of such radiation. If these absorption bands are presented as a chart, they can provide an effective material identification method. Absorption and transmission are directly linked to the chemical composition and crystal structure of the gem. About the visible spectral range, when comparing directly observed spectra we are familiar with to the ones recorded by spectrophotometers, it is important to underline that the sensitivity of human is not constant for the whole visible range. The sensitivity of the human eye is at maximum at about 550 nm and gradually decreases towards both longer and shorter wavelength directions. This fact leads to reduced perception of the bands closer to the visible range ends, while the CCD sensors equipping the modern UV-Vis-NIR units perform in a far more efficient way.

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

This is the second chart in G&G’s series focused on micro-features often observed in natural, treated, and synthetic gems. Sapphire (figure 1) was chosen because of its enduring importance within the gem trade. Demand for this gem species has been the driving force behind the development of treat ment techniques to improve natural stones and the continued production of inexpensive synthetics. Natural sapphires, which originate in certain ig-neous or metamorphic geologic environments are commonly treated to improve their color or clarity. The most common processes involve heat treatment to improve color. Synthetic sapphires have been pro-duced for more than a century, mostly by melt, flux, or hydrothermal solution methods (Hughes, 2017). All of these materials are widely encountered in the jewelry trade.

corundum, geology.11, Burma.12, jade, jadeite, fei cui, gems

The Mogok Metamorphic Belt is a north–south-aligned belt of mainly high-grade metamorphic rocks and granites that extends the length of Burma (Myanmar) along the western margin of the Sibumasu block from the Andaman Sea to the East Himalayan (Namche Barwa) Syntaxis (Figs 12.1 & 12.2). The Mogok metamorphic rocks host some of the world's finest rubies and sapphires, the former mainly from high-grade phlogopite + corundum marbles and the latter from a heterogeneous suite of syenite and charnockites that intrude the metamorphic rocks (Chhibber 1934a, b; Iyer 1953; Searle & Haq 1964; Bender 1983; Mitchell et al. 2007; Searle et al. 2007; Themelis 2008). Gem spinels are also found in forsterite-bearing marbles. Gemstones have been mined in the Mogok region since at least the mid-1800s (O'Connor 1888; Gübelin 1965a, b; Keller 1982, 1983; Kane & Kammerling 1992). Together with the adjacent Mergui Slate Belt these rocks lie to the west of the Shan Scarp and the Paung Laung-Mawchi Zone, interpreted by Mitchell et al. (2012) as a possible suture zone. We refer to this entire zone of metamorphic rocks, plus the Slate Belt and pre-collisional granites east of the Sagaing Fault and west of the Paung Laung-Mawchi Zone, as the Mogok–Mandalay–Mergui (MMM) Belt; the metamorphic rocks are referred to solely as the Mogok Metamorphic Belt (MMB).

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

corundum, inclusions.5, gems

corundum, Madagascar.12, gems

High quality blue sapphires have been mined in Myanmar for centuries (Kane & Kammerling 1992, Themelis 2001, Hughes 1997). Until the end of the 20th Century, sapphires were mined from the Mogok Stone Tract, mainly in the western area near Kyatpin and around Mogok town. Towards the end of the 20th Century blue sapphire mining extended to the west around Kyauk Pya That, Kabaing and Kin, to the north around Barnard Myo and in the Chaung Gyi valley, and in the east around Peint Pyit village (Themelis 2008, Hughes 2016). Between 2011 and 2016 new production from Baw Mar area started to reach the market and attracted the attention of gemologists visiting the region (Phyo Kan Nyunt et al., 2013). GIA field gemologists visited Baw Mar operations in 2013, 2014, and 2015. It was evident the mine was not only the highest altitude mine in the whole of the Mogok area but also one of Mogok’s largest mining operations. Its sapphire production is interesting and challenging for gemologists as, its sapphire characteristics (chemistry and internal features) are slightly different from the classic Burmese sapphires. The aim of this research project is to expand our knowledge of these gemstones which can be a challenge in terms of origin determination. During the field expeditions and subsequent laboratory work it became clear that even within the same mine, sapphires can look different to one another depending on the area where they are mined; samples from the southern area are generally lighter in color than the sapphires recovered from the northern part of the mine. In this study, we analyzed samples collected at the office (located near the mining site where the production was sorted) during two separate expeditions. The samples were mined from opposite parts of the mine, southern and northern, respectively. The general gemological characteristics; inclusions, UV-VIS and IR spectra and trace element chemistry are covered. A description of the mine, mining techniques employed and preliminary geological observations are also provided. Most of the data collected reveals sufficient information to differentiate between the two sampled areas within the same mine. It is clear that the Baw Mar sapphires formed in a complex geological environment with the potential to produce a range of qualities (high to low), various inclusion scenes and variable trace element concentrations.

gems, corundum, history.1, chemistry.2

This article presents a detailed history and exegesis of the 1798 paper by Charles Greville and Jacques-Louis Count de Bournon, “On the Corundum Stone from Asia,” which marked the first published argument that corundum was related to—or identical with—ruby and sapphire. It also introduced crystallography, recently developed in France, to a British scientific audience for the first time. René Just Haüy’s theory of the three-dimensional structure of minerals represented a novel extension of chemistry into the solid state. The case of corundum exemplifies the sophisticated mineralogy emerging in the late eighteenth century and the global scope of natural history as shaped by trade and empire. It also highlights how mineralogical debates began to transition from the private spheres of mining schools and elite collectors into broader public scientific discourse.

gems, corundum, Burma.12, quality.10

When British soldiers conquered Burma in 1885, they gave the last king hours to pack. Many of his treasures - heirlooms from a millennium of monarchy- were seized and sent to Britain. But the most precious, an enormous ruby, disappeared. Who took it, and where is it now?

gems, corundum, Madagascar.12, Bemainty

The discovery in Bemainty is not the rst one in the region. In 2015, rubies were discovered near Ambo-divoangy in Zahamena National Park and, in 2012, another rush took place at Ambohybe near Didy. In all cases, the trade was surprised with the quantity and the quality of the gems found since, previously, the region was mainly known for the ruby and sapphire deposit located east of Andilamena, which was the principal source of the lead-glass-lled rubies that ooded the market after. The trade has welcomed these new discoveries as they provided signi cant quantities of ne-looking gems. Yet, it is also realizing that the existence of these deposits could become a huge public-relations challenge for the indus-try because they are located in the Corridor Ankeniheny-Zahamena (CAZ), a protected area under the manage-ment of Conservation International (CI), one of the most powerful environental conservation groups in the USA with strong links to Hollywood celebrities (see Sidebar). This article summarizes eld expeditions undertaken by the author in the region since 2005. It describes the area’s deposits and highlights the challenges presented by illegal artisanal gem mining in areas set aside for conservation.

gems, early lapidaries, Albertus Magnus, French lapidaries, magical properties, medicine

The Middle Ages believed in the powers of precious stones: their medicinal and magical virtues were recorded in encyclopedic treatises known as lapidaries. This knowledge, inherited from Antiquity, endured for centuries: diamond grants invincibility; sapphire frees prisoners; emerald heals vision problems; amethyst protects against drunkenness; hematite stops bleeding, and so on. The powers attributed to stones operate by analogy—a mode of thinking that prevailed throughout the medieval period. This anthology of medieval lapidaries offers, for the first time, a bilingual edition of these long-dismissed and still largely unknown texts, with a selection of excerpts in Old and Middle French accompanied by their translation.