gems, corundum, Thailand.12, Inclusions.5

The mineral inclusions of alluvial ruby and sapphire from the Bo Welu gem deposit in Thailand’s Chanthaburi Province were collected and investigated. This deposit is directly related to a basaltic terrain. Raman spectroscopy and electron probe micro-analyzer (EPMA) measurements allow the identification of mineral inclusions of pyrope-rich garnet, sillimanite, high-Al diopside, sapphirine, nepheline, quartz, feldspar (mostly plagioclase), spinel, sulfide, anhydrite, and silicate melts in ruby and purple sapphire. Zircon, alkali feldspar (mostly with high Na content), monazite, columbite, and sulfide were identified in blue sapphire. This study represents the first report of several inclusions in ruby and sapphire from this gem deposit.The mineral inclusions of alluvial ruby and sapphire from the Bo Welu gem deposit in Thailand’s Chanthaburi Province were collected and investigated. This deposit is directly related to a basaltic terrain. Raman spectroscopy and electron probe micro-analyzer (EPMA) measurements allow the identification of mineral inclusions of pyrope-rich garnet, sillimanite, high-Al diopside, sapphirine, nepheline, quartz, feldspar (mostly plagioclase), spinel, sulfide, anhydrite, and silicate melts in ruby and purple sapphire. Zircon, alkali feldspar (mostly with high Na content), monazite, columbite, and sulfide were identified in blue sapphire. This study represents the first report of several inclusions in ruby and sapphire from this gem deposit.

gems, corundum, ruby, Thailand.12, Bo Rai

The Bo Rai alluvial gem field in Trat Province, eastern Thailand, was a major mining site for Thai ruby during the early 1980s, and this material continues to circulate in the gem market worldwide. For this study, approximately 1,000 Bo Rai ruby samples were examined and pre-screened for mineral inclusions. The rough stones usually formed platy, waterworn, tabular crystals with etched or resorbed surfaces. UV-Vis-NIR spectroscopy indicated a relatively high Fe content, which was confirmed by trace-element analysis. Solid inclusions typically consisted of Al-rich pyroxene, plagioclase and pyrope with subordinate sillimanite and spinel (both of which are reported here for the first time), as well as sulphides and silicate melt inclusions. The inclusion assemblage of pyroxene, plagioclase, pyrope and spinel closely resembles the mineralogy of mafic granulite xenoliths in alkali basalt associated with the Bo Rai gem field, which supports ruby formation in mafic granulite prior to being transported to the earth’s surface via basaltic eruptions.

gems, corundum, Ethiopia.12, sapphire, beryl, emerald, opal

Although Ethiopia is considered the cradle of mankind and the land of origins, gemstones never played a significant role in its long history and rich culture. Only in the last decade did Ethiopia emerge in the gem trade, with the discovery of large opal deposits near the town of Wegel Tena (Rondeau et al., 2010). When the first high-quality emeralds from Shakiso in southern Ethiopia reached the market in the fall of 2016, GIA’s Carlsbad and Bangkok labs conducted a joint preliminary study (Renfro et al., 2017). And in February 2017, GIA received news of a sapphire discovery near Aksum in northern Tigray Province (Vertriest et al., 2017). With all of this new material reaching the market, GIA collaborated with the Ethiopian Ministry of Mines, Petroleum and Natural Gas in Addis Ababa to set up an expedition to the sapphire, opal, and emerald sources. In March 2018, a team of four GIA gemologists and videographers traveled to Ethiopia to visit its gem sources. The first target was the sapphire deposit in the north, followed by the opal mines in the central highlands. The last area visited was near Shakiso to witness the developing emerald mines. During the expedition (figure 1), we documented mining techniques, social impact, material processing, natural challenges, and limitations. We also collected samples at the mines and nearby markets in accordance with GIA’s sampling protocols. These samples are now part of GIA’s reference collection and used for origin determination, research projects, and treatment experiments.

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, spinel, history, Tajikistan, balas ruby

Nice and well-illustrated article discussing the history of spinel from early times and on.

gems, corundum, sapphire, quality.10, Sri Lanka.12

At 422.66 carats, the Siren of Serendip blue sapphire is a sight to behold. Here, Rui Galopim de Carvalho FGA DGA shares the story behind this fascinating (and exceptionally large) gemstone and describes the process of setting it into a beautiful white gold and diamond necklace.

gems, corundum, spinel, Afghanistan.12, Tajikistan.12, Burma.12, Sri Lanka.12

Few books can be said to have changed the world but The Travels is one of them. Despite being written nearly 800 years ago, its epic scale and accounts of near-mythical exploits have ensured its continued popularity. This exceptional new edition reproduces Nigel Cliff's meticulous and accessible translation ‘the first English translation of the original text in nearly 50 years’ as well as his compelling introduction. Essential reading for newcomers to The Travels, it will also inform and entertain those familiar with the book. Adorned with decorative borders and chapter titles, the text is illustrated with the complete collection of 84 miniatures from the 1410 Duc de Berry manuscript housed at the Bibliotheque Nationale in Paris. A quarter-bound buckram binding and marbled paper sides add the finishing touches to this beautiful collector's edition.

gems, corundum, Mozambique.12, ruby, East Africa

Giard reports on the extraordinary development of ruby mining around Montepuez in northern Mozambique following the discovery of major deposits there in the late 2000s. The article describes the resulting “ruby fever,” which drew large numbers of artisanal miners, traders, and foreign buyers to the region, and the subsequent development of large-scale organized mining. It examines the exceptional quantity and quality of some Mozambican rubies, their rapid rise to prominence in the international colored-stone market, and the transformation of Mozambique into one of the world’s major ruby sources. Giard also addresses the economic and human consequences of the boom, including competition between artisanal miners and concession holders, security and illegal mining, local living conditions, and the challenge of ensuring that exploitation of this valuable gem resource contributes to sustainable development in the mining region.

gems, ruby, sapphire, beryl, emerald, jade, nephrite, spinel, Mughal jewelry

Treasures from the Al Thani Collection was an exhibition of artworks from the Al Thani Collection that was held at the Palace Museum in Beijing in 2018. The exhibition featured a diverse selection of artworks from different cultures and time periods. The exhibition featured artworks from antiquity to the early modern period. The exhibition included manuscripts, miniatures, metalwork, textiles, and jewelry. The exhibition included works from different civilizations, such as Egypt, China, Maya, and Cycladic. Sheikh Hamad bin Abdullah Al Thani is a member of the Qatari royal family and a distinguished collector. The first volume of the set documents the exhibition “The Gems and Jewels of India”. It is split into different sections including: The Mughal Treasury; Dynastic Gem and Jewels; Objects of Jade and Rock Crystal; Objects in Gold and Enamel; Regalia and Jewelled Ornaments; Cartier and the Great European Jewellers, and, finally, Contemporary Creations. The second and third volumes both document a second exhibition, held in 2018, entitled “Masterpieces from a Royal Collection”. Volume II focuses on ‘The Ancient World’ and ‘The Wider World’. The former includes Egyptian, Greek and Roman, Mesopotamian and Iranian works as well as Central Asian treasures, whilst the latter has objects from China, Pre- Columbian Central and South America, Africa and the Pacific. Volume III is split more specifically into ‘The Islamic World’ and ‘The European World’. Each theme is further devided into sub sections which cover all aspects of art including Manuscripts, Miniatures, Metalwork and Textiles, or Medieval Reliquaries, Limoges Enamels, Renaissance Jewellery, Rock Crystal and Wunderkammer objects, Silver, Jewellery (Cartier, Melerio, Chaumet, Bolin) and 54 pieces by Fabergé.

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.