corundum, Shandong sapphire, China.12, gems

Previous research has revealed that dark coloured Shandong sapphire is included by large numbers of micro-inclusions. Theoretical analysis of the results from the photometry and colourimetry of Shandong sapphires has shown that these inclusions have a scattering effect on the light incident on these sapphires. This scattering greatly reduces both the transmission and internal reflection of light from Shandong sapphire thus causing this sapphire to have a dark tone. During heat treatment, inclusions in Shandong sapphire create fractures that expand due thermal stress. This creates additional structural defects in this sapphire. In addition, some structural micro-inclusions in this sapphire increase in size during heat treatment so that they have a scattering effect on light. As a result of this research, it has been concluded that heat treatment can not improve the tone of Shandong sapphire. This research also has shown that scatter has a significant deleterious effect on the colours of gemstones

gems, jade, jadeite, fei cui, Mesoamerica, Mexico, Guatemala, Costa Rica, Mayans, Olmecs, Aztecs, archaeology, history, archaeogemology, China

Since jade was one of the most durable and evidently highly valued materials among the Classic Maya, as demonstrated by its depiction in art and its inclusion in royal tombs and caches, it possesses considerable analytical value for exploring systems of preference and restricted exchange within Maya society. This study uses jade datasets from Cancuén and Piedras Negras to examine the distribution, manufacture, and consumption of jade objects in two distinct geographic regions. The comparison between a city relatively rich in jade and another notably poor in jade has important implications for understanding the relative value of jade and the processes involved in its craftsmanship.

gems, garnet, pyralspite garnet, almandine, pyrope, Bohemia, Czech Republic

This study examines garnets from the Podsedice deposit in the České středohoří Mountains, mined for Bohemian garnet jewelry, revealing red pyrope with a brownish tint and rare dark violet Cr-rich pyrope. Electron microprobe analyses show the red pyrope consists of 74.3–75.1 mol% pyrope, 12.5–13.7 almandine, 4.3–7.2 uvarovite, 1.1–4.0 grossular, and 0.7–0.8 spessartine, with minor TiO₂ (0.44–0.77 wt%), Na₂O (0.05–0.10 wt%), and V₂O₃ (0.05–0.07 wt%). The violet variant contains 3.23–4.25 wt% Cr₂O₃. Both types show minimal zoning. Newly identified mineral inclusions include pargasitic amphibole, Al-Cr spinel, and Fe-Ni sulphide. Pargasite inclusions, 30–60 µm in size, show reduced Ca (~1.6 pfu) and elevated Na, suggesting ~20 mol% magnesiotaramite in the amphibole solid solution. These inclusions provide insights into the metamorphic conditions of the ultramafic host rocks prior to garnet formation. The garnets are notably inclusion-poor, and compositional data indicate derivation from pyrope lherzolites and peridotites in shallow crustal settings.

jade, nephrite, Taiwan, localities, gems

Green-colored nephritic jade artifacts are commonly found in Neolithic archaeological sites in Taiwan and some regions of the Philippines. Nephrite deposits only occur rarely in nature, and it is widely accepted that chemical analysis is required if nephritic artifacts are to be sourced to specific quarries. In order to define the mineralogical character of the Fengtian nephrite in Taiwan, an electron probe micro analysis (EPMA) was carried out on nephrites from this source and others in East Asia and the Pacific region. Seventeen nephrite specimens were analysed, and found to be composed of tremolite- actinolite amphiboles (Mg/[Mg+Fe] less than 0.93) with fibrous texture, and bearing chromian-spinel inclusions with significant amounts of manganese (Mn: up to 9 wt. %) and zinc (Zn: up to 7 wt. %). These chemical characters can be applied to differentiate the Fengtian nephrite from others.

gems, jade, jadeite, fei cui, Burma, fluid inclusions

A combined hydrogen-carbon-isotope and microthermometric study has been carried out on CH₄-bearing fluid inclusions in high-pressure jadeitites from the famous jadeite tract Myanmar. Two types of fluid inclusions were found in jadeites, large H₂O-rich and CH₄-poor inclusions and small H₂O-poor and CH₄-rich inclusions, thus indicating a possible entrapment of CH₄–H₂O fluids under unmixing conditions. Microthermometric results yield lower temperature limits for the entrapment of these fluid inclusions of ca. 300 to 400 °C. The bulk composition of the fluid inclusions is mostly H₂O (87 to 94 mol.% H₂O) and the isotopic composition of methane and water in the inclusions is characterized by δ¹³C(CH₄) values ranging from –30.1 to –25.5‰, and δD(H₂O) values ranging from –56.3 to –49.8‰. The stable isotope data would be indicative of an abiogenic mechanism of CH₄ formation; the occurrence of the jadeite veins in this paleo-subduction zone thus most likely point to the formation of these CH₄-bearing fluid inclusions by abiogenic thermal maturation of subducted organic carbon. These data not only provide evidence for cycling of organic carbon in paleo-subduction zones but also show that CH₄ not only occurs as shallow CH₄-rich plumes in accretionary prisms of recent subduction zones but also occurs in deeper portions of at least the upper 20 km of paleo-subduction zones.

corundum, geology.11, Australia.12, sapphire, Tasmania, gems

Alluvium and colluvium in the Weldborough area, NE Tasmania, yield sapphire, zircon and spinel, corroded by magma and abraded by alluvial transport. Drainage patterns and inferred palaeodrainage indicate the Weldborough basalts are the primary source. The Weldborough intraplate alkali basalts are fine-grained, olivine- and/or clinopyroxene-phyric with varying content of mantle and crustal xenoliths and xenocrysts. Despite extensive study, no sapphire or zircon megacrysts are found in the basalt or related clastic rocks. The Weldborough sapphires are blue (80%), yellow and green (20%) with rare pink sapphires. They contain olivine, feldspar, spinel, zircon, molybdenite and Nb–Ta-rich phases as mineral inclusions. The composition of zircon inclusions indicates the parental melt was highly evolved. Secondary olivine mineral inclusions are present. Primary fluid inclusions indicate a minimum trapping pressure of 4.5 kbar at 1000 to 1200 °C. LA-ICP-MS analysis indicates the sapphires have iron (2,590 ppm), titanium (383 ppm), gallium (258 ppm) and tantalum (186 ppm) as the most abundant trace elements. Niobium, beryllium, magnesium, vanadium, chromium and tin are low-level trace elements in the Weldborough sapphires. Beryllium, titanium, niobium and tantalum are enriched in the cores of the sapphires. Two element associations were recognised in the sapphires: an Fe–V–Ga association and an Nb–Ta–Be association. The Nb–Ta–Be association is typical of input by an incompatible-element-rich melt such as a granite pegmatite or a carbonatite. The sapphires have O-isotope values of +4.4‰ to +6.3‰, indicating they are in O-isotope equilibrium with rocks of mantle O-isotopic compositions, and little or no crustal interaction is inferred in the source. The zircon inclusions in the sapphires have a U–Pb age of 47 ± 4 Ma, which is identical to the age of the Weldborough basalts (46.8 ± 0.6 Ma). The zircon inclusions have been reset during entrainment in basaltic magma. The Weldborough sapphires were entrained and brought to the surface by the Weldborough basalts 47 million years ago. The Weldborough basalts are the source of sapphire, spinel and zircon found in the Ringarooma, George and possibly the Boobyalla River catchments. The broad range of trace element and inclusion data reported here support an origin for the sapphire in shallow parts of the underlying mantle. Corundum consists of Al₂O₃, has a high hardness (9) and high specific gravity (~4). Corundum’s hardness and chromophoric lattice substitutions make it a valuable gemstone in the form of sapphire and ruby, and important as an abrasive in the form of emery. Corundum occurs in a wide variety of igneous and metamorphic rocks and is commonly found in detrital deposits due to its hardness. In metamorphic rocks, corundum is found in metamorphosed laterites, partially melted pelitic rocks, high-Mg and high-Al schists, Si-poor hornfels within the aureole of igneous intrusions, and metamorphosed marbles. In metamorphic rocks the presence of corundum reflects a silica-undersaturated, alumina-rich paragenesis. Corundum, as an accessory mineral in igneous rocks, is found in monzonite, syenite and nepheline syenite, ultramafic dikes, and other pegmatitic dikes. The presence of corundum as an accessory mineral in igneous rocks is an indication of silica undersaturation in parent magma or a post-intrusive desilicification process. A major source of gem-quality corundum is detrital deposits sourced from alkali basalt terrains. The formation of alkali basalt-hosted corundum involves two stages: the formation of corundum and the subsequent incorporation and expulsion via intraplate basaltic volcanism related to rifting. The genesis of the corundum xenocrysts has been debated and no single model is able to satisfactorily explain the genesis of poly-modal gem fields. For alkali basalt-hosted corundum, the favourable model for sapphire formation is the plutonic crystallisation at lower crustal/upper mantle depths from a highly aluminous, volatile- and trace element-rich alkaline parental magma. Alkali basalt-hosted rubies are likely to form from the metamorphic recrystallisation of mafic rocks in the upper mantle.

gems, Russia, Siberia, pegmatite, quartz, tourmaline, locality, species, Transbaikalia

In the Oktaybrskaya pegmatite of central Transbaikalia, coexisting melt (MI), fluid-melt (FMI), and fluid (FI) inclusions in quartz were studied to reconstruct pocket formation conditions using thermodynamic modeling of PVTX-properties of orthoboric-acid aqueous fluids. Early-stage quartz from both pocket zones and host pegmatite contains FMI with crystalline aggregates and orthoboric-acid-rich fluids, though FMI become rarer and fluid volumes increase in later quartz growth zones, disappearing entirely at the latest stage. These FMI exhibit variable solid/fluid ratios from heterogeneous trapping of coexisting melts and fluids. Raman, SEM-EDS, and EMPA analyses show aggregates mainly consist of boron-rich micas (muscovite–nanpingite series), lepidolite, and minor topaz, quartz, K-feldspar, and unidentified phases. FI and FMI fluids share similar salinity (4–8 wt.% NaCl eq.) and H₃BO₃ content (12–16 wt.%). MI homogenize at 570–600 °C, while large FMI with silicate crystals melt at 615 °C but remain non-homogeneous even after 24 h at 650 ± 10 °C and 2.5 kbar, retaining glass+crystals or fluid+glass textures. FMI glasses are enriched in F (1.94–2.73 wt.%), B₂O₃ (2.51 wt.%), Cs₂O (3.64–5.20 wt.%), Li₂O (0.54 wt.%), Ta₂O₅ (0.57 wt.%), Nb₂O₅ (0.10 wt.%), BeO (0.12 wt.%), and >12 wt.% H₂O, indicating highly evolved residual melts from late magmatic stages. Microthermometry suggests crystallization temperatures of 615–550 °C. Quartz–feldspar matrix crystallization generated residual melts and fluids enriched in H₂O, B, and F, forming chemically distinct pockets with varying internal pressures. Progressive crystallization led to further fluid exsolution and pocket overpressure, which, in turn, caused fracturing and “fluid explosions,” linking pockets, mixing fluids, and inducing autometasomatic alteration and formation of complex “primary–secondary” pockets.

gems, spinel, star spinel, Sri Lanka

Four-pointed or six-pointed star sometimes can be seen in a spinel, but it is rarely reported that there are multiple groups of asterism on the same spinel. In this article, the spinel with both four groups of six-pointed star and three groups of four-pointed star have been studied by means of conventional gemmological techniques, Raman spectroscopy and electron probe. The experiments indicate that there are multiple groups of parallel needle-like inclusions in spinels, which result in the multiple groups of asterisms at the same spinel.

corundum, geology.11, Vietnam.12, , gems

This article compares the gemological characteristics and geologic setting of rubies from Luc Yen and Quy Chau in northern Vietnam. At Luc Yen, rubies occur as dissemi-nated crystals in small veinlets or fissures within marbles of Upper Proterozoic to Lower Cambrian ages. Secondary ruby deposits occur in associated alluvial gravels. At Quy Chau, the economic ruby and sapphire deposits are found only in placers.. The ruby crystals from Luc Yen examined were typically hexagonal bipyramids, whereas those from Quy Chau commonly formed short hexagonal prisms. Compared to the Luc Yen material, the color of the Quy Chau rubies was usually more saturated and showed a stronger red fluorescence to long-and short-wave UV radiation. R.I. values of rubies from both areas were 1.762–1.770 (birefringence ~0.008). S.G. values for samples from Luc Yen were 3.92–4.01, whereas those from Quy Chau were 3.94–4.05. Rubies from both areas exhibited twinning, straight and angular growth zoning, and (in some instances) various forms of color zoning. The most common mineral inclusions in material from both localities were apatite, calcite, dolomite, rutile, diaspore, phlogopite, and zircon. Three kinds of fluid inclusions (both primary and secondary) also were found. The inclusion characteristics and geologic settings indicate that rubies from these deposits are the result of high-grade (amphibolite facies) regional metamorphism.JES

corundum, history.1, chemistry.2, gems

Gemstones set on ancient jewels are invaluable witnesses from the past, and to obtain these prized items, humans established long-distance trade routes whose extension and historical evolution pose major archaeological questions; chemical characterisation has proven especially useful in this context, as the elemental composition reveals the gem’s identity—such as SiO₂ for quartz, Al₂O₃ for ruby and sapphire, or Be₃Al₂Si₃O₁₈ for emerald—while trace element patterns, when compared to reference samples, may indicate geographic origin; however, such analyses must be non-invasive (requiring neither sampling nor dismounting) and non-destructive (leaving no damage), and ion beam techniques like PIXE (particle-induced X-ray emission) and PIGE (particle-induced γ-ray emission) satisfy these demands by operating directly on the surface in air with 20 μm resolution—PIXE detecting elements heavier than sodium with sensitivity to the μg/g level, and PIGE extending coverage to light elements (Li, Be, B, F); additionally, Raman micro-spectrometry is employed to identify inclusions beyond the reach of the ion beam, as these features often inform provenance in gemmology; the combined use of external beam PIXE/PIGE and Raman spectroscopy is demonstrated in this study through analyses of ancient rubies from a Mesopotamian statuette and of emeralds and garnets set in Barbarian jewels from the Dark Ages.