gems, corundum, inclusions.5, photomicrography, inclusions, Burma, Burmee gems, ruby, sapphire, spinel, tourmaline, peridot, topaz

Inclusions of various gems found in Burma's Mogok Stone Tract.

gems, beryl, emerald, China, Zhen'an, Shaanxi

In 2017, the first emerald deposit in the Qinling Orogenic Belt was found in Zhen’an County, Shaanxi Province, China. This study presents a comprehensive analysis of the gemological, spectroscopic, and trace element characteristics of a select set of Zhen’an emerald samples based on standard and advanced gemological methods, including gem microscopy, ultraviolet/visible/near-infrared spectroscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, and laser ablation–inductively coupled plasma–mass spectrometry. Microscopic studies revealed that Zhen’an emerald exhibits longitudinal striations and inclined growth steps on its hexagonal prism faces and contains an abundance of two-phase (gas/liquid) fluid inclusions. A variety of mineral inclusions were identified, including phlogopite, plagioclase, scheelite, calcite, talc, and hematite. Some crystals display color zoning, with a deeper green rim containing elevated vanadium and iron. Zhen’an emerald’s dominant chromophore is vanadium, and the material is characterized by a high vanadium concentration, notably low chromium, a moderate iron concentration, and an elevated ratio of gallium to cesium. These unique geochemical signatures of Zhen’an emerald, along with their internal features, could be a robust tool for discerning emerald from this deposit.

gems, corundum, Australia.12, zircon, geology.11, New England District

Transparent pale yellow to brown zircon megacrysts occur with gem corundum in alluvial deposits linked to alkali basalts of the Inverell–Glen Innes District, New South Wales, Australia. Previous LA-ICP-MS analyses of zircons from Kings Plains, Mary Anne Gully, and Swan Brook showed chemical homogeneity and yielded two age groups: 216–174 Ma (Late Triassic–Early Jurassic) and 45–37.7 Ma (Eocene). New U-Pb dating of zircon inclusions in gem-quality blue sapphires produced concordant ages of 37 ± 1.7 Ma (Kings Plains) and 35.1 ± 1.6 Ma (Mary Anne Gully), matching the 38–33 Ma K-Ar ages of the Maybole volcanic suite and aligning with the younger zircon population. These results, together with gemmological and chemical evidence, demonstrate a genetic connection between sapphire crystallisation in the deep crust or mantle and subsequent transport to the surface by alkali basaltic magmas.

gems, corundum, USA.12, Montana.12, chemistry, geology.11

Montana hosts the largest sapphire deposits in the US, but the genesis of and connection among the various secondary and primary sapphire occurrences remain cryptic. In situ SIMS measurements of oxygen isotopes in sapphires and zircon inclusions in sapphires provide an opportunity to study the isotope and trace element geochemistry in order to understand sapphire-forming protoliths (i.e. crustal setting and alteration). Sapphire from Montana was transported as xenocrysts in carrier (host) magmas that resorbed sapphire exteriors during transport. The timing and nature of sapphire genesis is elucidated by SIMS measurements of trace elements and U–Pb from discrete zones in zircon inclusions with rims that are interpreted to be syngenetic with host sapphire. Montana sapphires exhibit a large range of δ¹⁸O values, from −3‰ to +12‰ VSMOW. However, all but two anomalous crystals fall in the range of 0‰ to 8‰. There is significant crystal-to-crystal variability yet averages at most deposits are consistent with high-temperature equilibration with the mantle (δ¹⁸O(Crn) = 4.4‰ to 5.7‰), with the exception of the commercial sapphire deposits at Rock Creek that average 2.7‰. Ruby analyses are limited, but typically have lower δ¹⁸O values compared to sapphires from the same detrital localities. Homogeneity within individual crystals (avg. 2σ = ±0.2‰) indicates the absence of isotopically distinct fluid or melt during crystallization. But intercrystalline δ¹⁸O ranges by up to 7‰ at a single locality, suggesting sapphire variability at a deposit reflects heterogeneity in the original protolith. Oxygen isotope fractionations between zircon rims and surrounding sapphire suggest comagmatic zircon inclusions and corundum equilibrated at high temperature. No correlation is seen for the degree of radiation damage and alteration of δ¹⁸O(Zrc) when zircon inclusions are surrounded and armored by sapphire. U–Pb ages and trace elements were measured in a small subset of syngenetic zircon inclusions in Dry Cottonwood Creek sapphires, revealing a Proterozoic (1778 ± 9 Ma) age for the protolith of sapphires at this locality and a likely polygenetic history. Previous work has suggested formation of these sapphires through partial melting of anorthosites and several anorthosites occur locally and match the age of zircon inclusion cores — the Boehls Butte anorthosite (∼180 km NW of Rock Creek) and the Bitterroot anorthosite (∼55 km W of Rock Creek) could correlate with Al-rich protoliths at depth. Proterozoic U–Pb ages of zircon from the Boehls Butte anorthosite (1787 ± 2 Ma) match well with the age of zircon inclusion cores in Dry Cottonwood Creek sapphires and suggest genesis in these or similar protoliths. Zircon rims with Tera-Wasserburg lower intercept ages of 110 ± 9 Ma are consistent with previous observations of a xenocrystic relationship to the ∼50 Ma Eocene volcanic rocks. Corundum that formed over 50 Ma prior to being scavenged by Eocene magmas likely originated by the anatexis of Precambrian anorthosites and possibly other aluminum-rich rocks at depth.

gems, beryl, emerald, use of emerald in China

Emerald is one of the five internationally recognized precious gemstones, highly favored by people for its unique color and charm, and holds an important historical position in China. This article is based on archaeological discoveries of Chinese emeralds and combined with clues from ancient literature to explore the time, evolution of name, usage pattern, and source of emerald in China during the Ming Dynasty. It is found that although there was exchange and interaction of coloured gemstones between China and Central and Western Asia during the Han and Wei dynasties, it was not until the Yuan and Ming dynasties that emerald were discovered in China.Emerald entered China through trade, tribute, and other means, and was accepted by China. Its name was transliterated from a foreign language and gradually evolved from Zhumula" and "Zumula" to "Emerald", which is still used today. Through gemmological and spectroscopic testing of the unenset emeralds unearthed from the tomb of Liangzhuang King, it was found that the inclusion characteristics and mass fraction characteristics of the emerald in the tomb of Liangzhuang King were similar to those in Egypt and Austria, such as FeO, MgO, Cr2O3, V2O3, etc. Based on the historical background and the premise that the emerald from the tomb of Liangzhuang King was brought back through the Maritime Silk Road, it is believed that the emerald may have originated from Egypt or Austria. Although emerald entered China relatively late, it held an important position in the social and cultural context of the Ming Dynasty. As a precious gemstone material, emerald was mainly used for leather belt decoration by nobles, reflecting to some extent the hierarchical system in the ritual system and becoming a symbol of social status."

gems, spinel, Burma, Myanmar, Tajikistan, Tanzania, Vietnam, color, spectra, PL spectra

Gem-quality spinel is an important category of gemstones. Currently, deposits such as Mansin, Namya, and Mahenge, known for yielding high-value single spinel crystals, have appeared. Over the past five years, there has been over 200% increase in the number of papers related to spinel compared to the previous five years. Current research mainly focuses on using geochemical analysis and inclusions characteristics for provenance tracing; however, there are shortcomings such as overlapping discriminant features and the absence of inclusions in gem-quality spinel. Therefore, delving into the crystallographic properties and its application in rapid non-destructive testing of spinel are conducive to the developing provenance tracing technologies suitable for the domestic quality inspection industry, which is of great significance for the domestic gemmological research and industry development. PL spectrum of spinel is constituted by a series of N-lines, each of which is associated with the arrangement of PL centers of Mg²⁺ and Al³⁺ in spinel. This laid a solid foundation for the application of PL spectrum of spinel. Based on the ordered-disordered phase transition characteristics of spinel, our research group has demonstrated in preliminary studies that the ratio of the R peak (ordered peak) to the N peak (disordered peak) in PL spectrum of spinel can finely reflect the degree of disorder, and established a thermodynamic model to quantitatively calculate its thermal history (closure temperature). In this study, 308 red spinel samples from Myanmar, Tanzania, Vietnam, and Tajikistan (Fig. 1) were studied. The main results are as follows: (1) Validation of method applicability. This study has demonstrated that even when chromium content of spinel is below the detection limit of LA-ICP-MS, it may also detect the PL spectrum of Cr³⁺ within the spinel (Fig. 2). This indicates extremely high PL efficiency of Cr in spinel, proving that our research method is not only applicable to red spinels but can also be broadly applied to the majority of gem-quality spinels. (2) Based on quantitative and qualitative analysis methods, the photoluminescence spectral characteristics of chromium ions in spinels from each locality were summarized, selecting spectral features significant for provenance identification. Under liquid nitrogen test conditions, spinels from all four localities exhibited four common N peaks of N1, N3, N2, and N5, within the zero-phonon line range (14 480–14 640 cm⁻¹) (Fig. 3). Meanwhile, Tanzanian spinels could be further subdivided into types I and II based on the feature of N2 peak. (3) Quantitative calculations of the ordered-disordered phase transition equilibrium constants (k values) and closure temperatures of spinel samples from four localities were applied to determine discriminant for provenance tracing. The k values of Tanzanian spinels range from 1.13×10⁻⁶–2.47×10⁻⁴; Tajikistan spinels range from 1.75×10⁻⁵–2.85×10⁻⁴; Vietnam spinels range from 1.29×10⁻⁵–3.13×10⁻³; Myanmar spinels range from 1.03×10⁻⁴–2.65×10⁻³. The results indicate that the degree of disorder of spinel crystals from four localities is Myanmar/Vietnam > Tajikistan > Tanzania. Moreover, combining with statistical methods, the closure temperature ranges of spinels from four localities were obtained: Tanzanian spinels range from 1 057 K to 1 072 K; Myanmar spinels are from 1 196 K to 1 218 K; Tajikistan spinels are from 1 128 K to 1 141 K; Vietnam spinels are from 1 057 K to 1 250 K. In summary, this study has summarized equilibrium constants for ordered-disordered phase transitions, closure temperatures, and spectral features with provenance tracing significance based on PL spectrum of ions in spinel. We have not only accumulated a large amount of reliable data but also further optimized data analysis methods in quantitative calculation and statistics. These achievements have validated the practical application feasibility of our preliminary theoretical research and advanced the development of spinel provenance tracing technology. Meanwhile, this also advanced the development of the researches in using spinel as a medium to constrain geological thermal history.

gems, corundum, USA.12, Montana.12, chemistry, geology.11, inclusions.5

A new, comprehensive approach to characterizing detrital corundum in sediments and placer deposits is outlined and applied to a sample of poorly sorted, mud-supported colluvium rich in rhyolite tuff clasts from the sapphire-producing layer at Gem Mountain Mine, Rock Creek, Montana. High angularity and the predominance of inherited surface features indicate that corundum was not abraded during transport, consistent with deposition by mass wasting. Corundum grain abundances per 10 kg of sediment (rounded to nearest whole number) are as follows: 4–8 mm (1 grain), 2–4 mm (12 grains), 1.0–2.0 mm (10 grains), 0.5–1.0 mm (43 grains), 0.25–0.50 mm (90 grains), 0.125–0.250 mm (480 grains), and <0.125 mm (55 grains; underrepresentation due to poor recovery). The ∼ 50× abundance of corundum in <2 mm size fractions relative to the >2 mm size fraction of potential economic interest suggests that fine-grained corundum may have potential as a pathfinder for gem corundum deposits in heavy mineral surveys. Corundum grains are transparent and divided into four types by surface texture and extent of crystal face development: (1) rounded with frosted surface, anhedral/subhedral; (2) angular with hillocky/irregular surface, anhedral/subhedral; (3) angular subhedral grains with glassy curved faces; and (4) angular, idiomorphic blue grains (all <1 mm). Surface texture Types 1–3 occur in pastel-colored corundum (green, yellowish-green, yellow, colorless) and are the result of dissolution subsequent to euhedral crystal growth. Mineral inclusions in corundum include: pastel corundum – biotite (variable Fe, Mg, Ti, F contents), plagioclase feldspar (andesine-labradorite), rutile, hercynite; blue corundum – alkali feldspar, rutile, zircon, ilmenite, apatite, spinel. Corundum uncommonly occurs in composite grains with biotite, plagioclase, and K-feldspar. Rhyolite occurs as a partial encrustation on one corundum grain. Rock Creek corundum may have originated from partially melted metapelite in a metamorphic basement, and incorporated and transported to the surface by rhyolitic magmas. Due to scant geologic context and an absence of radiometric age data, the proposed genetic model remains highly speculative.

gems, beryl, emerald, Egypt

In the present study, rough emerald single crystals and rough emeralds in the host rock from the ruins of Alexandria and from Mount Zabargad in Egypt, preserved in the collection of the museum of the Ecole des Mines (Mines Paris—PSL) since the late 19th or early 20th century, are investigated. All samples were characterized by non-destructive spectroscopic and chemical methods during a week-long loan to the LFG. Raman, FTIR and UV-Vis-NIR spectroscopy revealed that Egyptian emeralds contain H₂O molecules accompanied by relatively high concentrations of alkali ions and are colored by chromium and iron. Additionally, EDXRF showed that the emeralds from Egypt contain up to 84 ppm Rb and low amounts (below 200 ppm) of Cs. Inclusions and parts of the host rock were also observed under optical microscope and analyzed with Raman spectroscopy. Tube-like structures, quartz, calcite, dolomite, albite and phlogopite are associated minerals, and inclusions are identified in these historic emeralds from Egypt. This work will hopefully further contribute to the characterization of emeralds of archaeological significance.

gems, spinel, Vietnam, Luc Yen

Yên Bái in northern Vietnam is a new source of pink spinel, yet research on spinels from this locality remains limited. In this study, pink spinel samples from Yên Bái were systematically examined using conventional gemmological instruments, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), ultraviolet-visible absorption spectrophotometry, fluorescence spectrometry, and other analytical techniques. The results showed that the spinels from Yên Bái exhibit poor roundness, and some retain their original crystal habit. The samples range from transparent to translucent, with strong fluorescence and surface etching. Rich solid and liquid inclusions were observed under the microscope, including octahedral inclusions, tubular inclusions, and numerous fluid inclusions distributed along healing fissures. The UV-Vis absorption spectra were generally consistent across samples; however, magenta-colored stones could be distinguished from others by their low vanadium and high iron content. Most samples exhibited strong pink fluorescence, with slight variations in intensity. Two-dimensional fluorescence spectra were largely consistent and showed characteristic Cr³⁺ emission lines. Chemically, the main constituents were MgO and Al₂O₃, with SiO₂ ranging from 0.70% to 1.06% and CaO content below 0.1%—a typical signature of spinel from dolomitic-marble-type deposits. Compared to marble-hosted pink spinels from other regions, the Yên Bái material can be distinguished from spinels from Tajikistan and Tanzania based on trace elements such as Fe/Sn, Ni, and Zn, though partial overlap exists with spinels from Myanmar.

gems, spinel, inclusions, Sri Lanka

A comprehensive mineralogical and gemological study was conducted on 340 unheated spinels from Sri Lanka, specifically from the mining areas of Horana, Eheliyagoda, Ratnapura, and Okkampatiya. Sri Lankan spinels exhibit a wide range of colors, including the commonly seen pink to purplish pink, as well as green and blue hues. Compared to spinels from other regions like Myanmar, Vietnam, and Tanzania, Sri Lankan spinels are notably richer in inclusions. Common inclusions across the studied areas include dolomite, apatite, zircon, and chondrodite. Additionally, spinels from Horana contain graphite and forsterite, while those from Okkampitiya include graphite and rutile. Partially healed fissures are prevalent in Okkampitiya spinels, but unlike Vietnamese spinels, dislocations and growth structures are generally absent. LA-ICP-MS analyses revealed no significant geochemical differences among the mining regions, though cobalt-blue spinels showed Co concentrations ranging from 11 to 120 ppm. UV-visible absorption spectra demonstrated variable contributions of Cr³⁺, V³⁺, and Fe²⁺, which account for the spinels’ color variations from pink, red, and orange to purple and blue-green. Infrared and Raman spectroscopy confirmed that none of the analyzed samples showed evidence of heat treatment.