gems, spinel, Burma, Myanmar, Tajikistan, Tanzania, Vietnam

Most pink-to-red spinel that is currently available on the global gem market originates from moderate– to high–grade metamorphic rocks. For this study, we characterised 60 such spinels from Myanmar, Tajikistan, Tanzania and Vietnam. They ranged from pink to red with orange or blue modifiers due to combinations of the chromophores Cr³⁺, V³⁺ and Fe²⁺. The most common mineral inclusions in the samples from Myanmar, Vietnam and Tanzania were apatite crystals and graphite platelets, and we also observed zircon in the spinels from Tanzania. Octahedral negative crystals and partially healed fractures were present in samples from all four origins, while dislocations/needles were found only in those from Tanzania and Vietnam. Linear discriminant analysis of chemical data obtained by LA–ICP–MS was performed using seven elements (Ti, V, Cr, Fe, Zn, Ga and Sn) and provided potential criteria for separating spinels from these four important localities.

gems, tourmaline, inclusions

Tourmaline is well known for its range of colours, but not so much for its variety of inclusions. Most of the time it simply contains elongated filamentary two-phase fluid inclusions referred to as ‘trichites’. While cataloguing some older samples in the collection of the French Gemmological Laboratory, we came across a tourmaline of unknown geographical origin that contained some unusual octahedral inclusions (Figure 8).

gems, spinel, bi-colored spinel

Buathong and Narudeesombat describe a rare natural spinel with distinct purple and greenish blue zones, investigating its identity, colour mechanisms, chemical composition, and treatment status. Submitted to the GIT Gem Testing Laboratory, the faceted specimen weighed 0.57 ct and measured 7.02 × 3.32 × 2.27 mm. It was singly refractive, with a refractive index of 1.718 and hydrostatic specific gravity of 3.60, consistent with spinel. Microscopy revealed oriented arrays of short to elongated iridescent silk and minute particles in the purple zone, while the greenish blue portion contained no observed inclusions. Both zones were inert under long- and short-wave ultraviolet radiation. Ultraviolet–visible–near-infrared spectroscopy showed absorptions at 371, 386, 458, and 555 nm in the purple zone. The greenish blue zone displayed corresponding features together with additional broad bands at approximately 656 and 917 nm. These absorptions were interpreted in terms of ferrous iron, ferric iron, and intervalence charge transfer between them. In the purple region, iron-related absorption leaves a blue-violet transmission window, while decreasing absorption towards the red contributes to the observed purple colour. Stronger short-wavelength absorption and the broad intervalence charge-transfer band near 656 nm instead produce a blue-green transmission window in the greenish blue region. The authors infer somewhat greater concentrations of ferrous and ferric iron in that zone, consistent with its higher measured total iron content. Semi-quantitative energy-dispersive X-ray fluorescence analysis identified magnesium and aluminium as major constituents, minor iron, silicon, and zinc, and traces of vanadium, chromium, and gallium. Total iron, expressed as Fe₂O₃, was 2.56 wt.% in the purple portion and 2.77 wt.% in the greenish blue portion; zinc oxide was 1.01 and 0.69 wt.%, respectively. Photoluminescence spectra obtained with 532 nm laser excitation showed a closely matching series of sharp chromium-related emission centres in both zones. These features were consistent with chromium substituting for aluminium in octahedral sites, and their sharpness supported identification as unheated material. The combination of characteristic inclusions, significant zinc content, physical properties, and photoluminescence behaviour established the specimen as natural, unheated spinel. The report documents how chemical differences and associated iron absorption can produce contrasting colours within a gem species in which a wide overall colour range is common but bicoloured specimens are scarce.

gems, corundum, treatments.6, diffusion

A 1.94 ct cushion-cut blue sapphire was submitted for confirmation of treatment and identified as corundum using a GemmoRaman-532SG spectrometer. The stone exhibited a pale violetish blue body colour and deep reddish pink surface-related colouration restricted to the table and a small area along the pavilion. Microscopic observation revealed fingerprint inclusions, confirming the natural origin of the sapphire. Although the unusual colour distribution initially suggested a coating treatment on selected surfaces, careful microscopic examination showed that the pink colouration diffused slightly below the surface. Energy-dispersive X-ray fluorescence (EDXRF) spectroscopy indicated significant chromium (Cr), and the pink areas exhibited red fluorescence under long-wave ultraviolet excitation, unlike red-coated stones previously examined by the authors. These observations were consistent with chromium-diffused corundum. Infrared spectral features recorded using a GemmoFtir spectrometer confirmed that the sapphire had been heat treated, suggesting that red surface diffusion had been applied and that most of the diffused layer had subsequently been removed by polishing. However, the reason for retaining the diffusion treatment on only some surface areas remained unclear, given the resulting unnatural appearance. The case documents a natural blue sapphire with partial red surface diffusion and highlights the identification of this treatment through microscopic examination, EDXRF spectroscopy, ultraviolet fluorescence, and infrared spectroscopy. The authors also suggest that previously treated stones may be polished to remove near-surface treatments as demand for pale-coloured gemstones increases, potentially leading to more frequent encounters with such material.

gems, corundum, Afghanistan.12, inclusions.5, blue sapphire

Rutile, titanium dioxide (TiO₂), is a tetragonal mineral that generally occurs in corundum as silk (exsolution-formed needles), dust-like exsolution particles, or macroscopic crystal inclusions. Rutile crystals can have orange to deep red-brown coloration, and the crystal shapes can be rounded or euhedral. The author recently examined a 4.24 ct faceted transparent blue sapphire from Afghanistan. The stone contained dusty flake-like inclusions, naturally healed fractures, lathe-like inclusions, twinning, rounded colorless crystals identified as apatite (RRUFF R040098), and an unusual long prismatic orange crystal identified as rutile (RRUFF R040049). This rutile crystal shape is not typical for corundum, particularly in blue sapphire.

gems, corundum, ruby, Burma.12, inclusions, lazurite

A parcel of small rubies was received for identification at the S Gemmological Institute (SGI) gem lab in Yangon, Myanmar. Based on chemical, spectroscopic, and standard gemological testing, they were determined to originate from the Mogok Stone Tract in Myanmar. One faceted ruby contained a small blue crystal inclusion with what appeared to be a pyritohedron shape but an uncommonly seen bright blue color (figure 9). This inclusion was identified by Raman spectroscopy as lazurite. A blue lazurite inclusion was previously reported to have been found in a 5.09 ct Burmese ruby and a 1.40 ct ruby from Namya, Myanmar (Spring 2012 Lab Notes, pp. 51–52). Also, blue lazurite mineral has previously been detected in 1.02 ct light gray Burmese spinel (Spring 2019 Micro-World, pp. 112–113). According to the literature and our knowledge of inclusions in rubies from Mogok, this blue mineral is rare as an inclusion in Burmese rubies.

gems, corundum, inclusions.5, Mozambique.12

Discovery of staurolite in Mozambique ruby.

gems, beryl, emerald, Russia, Malysheva, Russian beryl, emerald mines, Ural Mountains, inclusions

Russian emeralds have been mined since the mid-nineteenth century near Yekaterinburg in the Ural Mountains. They are classified as schist-related emeralds, meaning they formed in the reaction zone of a pegmatite intruding into schists. Similar emeralds are found in Zambia, Brazil, and Ethiopia. All of these deposits can show a similar inclusion scene (S. Saeseaw et al., “Geographic origin determination of emerald,” Winter 2019 G&G, pp. 614–646). A 1.489 ct Russian emerald crystal collected by GIA at the Mariinsky Priisk mine showed several interesting included crystals. The crystals appeared as long yellowish brown rods (figure 6). In some cases, they appeared as a group of disordered coarse needles (figure 7). They were identified by Raman spectroscopy as rutile. Although rutile crystal inclusions are common in schist-related emeralds, this crystal morphology is unusual and has not previously been mentioned in the literature. Therefore, this inclusion might be unique and different from the other schist-related emerald sources. These unusual patterns could potentially be an indicator of Russian origin.

gems, beryl, emerald, Pakistan, emerald inclusions, emerald spectroscopy

In this paper, the inclusions and the structural water in the microchannel in emeralds from Pakistan were investigated by using optical microscopy, infrared microspectroscopy (FTIR), Raman spectroscopy, and electron microprobe analyzer (EPMA). The emeralds from Pakistan contain type I and type II waters. The infrared spectra show that the intensity of water type II (5270, 3600, 1632 cm⁻¹) is much stronger than water type I (1600 cm⁻¹). Most of the multiphasic inclusions in these emeralds are of biphasic elongated shape or are “neck-licking” inclusions, which consist of liquid (H₂O) and gas, including carbon dioxide gas (CO₂) + nitrogen (N₂) + methane (CH₄). The main solid inclusions are magnesite, dolomite, muscovite, and quartz. These inclusions and infrared spectra contribute to distinguishing Pakistani emeralds from emeralds of other origins.

gems, spinel, Burma, inclusions

Providing the famous “Jedi” spinel, Man Sin (Myanmar) has gained more and more attention in these years. Gem microscope and Raman spectrometer were used to carefully test inclusions in spinels. The multi-phase inclusion containing orange-yellow fluid could help distinguish Man Sin spinels from the spinels of other localities. The orange-yellow fluid was found in octahedral negative crystals and on the surface of mineral inclusions, which could form the indicating multi-phase inclusions with H₂S (gaseous and liquid) and a variety of minerals. The Raman spectrum of the orange-yellow fluid shows four bands at 155, 220, 443, 475 cm⁻¹ which indicate that it is high-level natural sulphur solution and the liquid is probably CS₂. Sulphur indicates highly reducing conditions during the formation of spinels from Man Sin, Myanmar.