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.

gems, corundum, treatments.6, Madagascar.12, heat treatment, Ilakaka, zircon inclusions, microraman

The present study is focused on the analysis of zircon inclusions found in pink to purple sapphires from Ilakaka (Madagascar) with an optical microscope, Fourier-transform infrared (FTIR), and micro-Raman spectroscopy in order to update previous knowledge and find insights to separate heated from unheated samples. In total, 157 zircon inclusions in 15 unheated samples and 74 zircon inclusions in 6 heated samples are analysed using micro-Raman spectroscopy with standardised parameters. The full width at half maximum (FWHM) of the main Raman band due to anti-symmetric stretching vibration ν₃ of the SiO₄ tetrahedron in the zircon structure has been carefully measured. In the unheated samples, it ranges from 6.26 to 21.73 cm⁻¹ with an average of 10.74 cm⁻¹, a median of 10.04 cm⁻¹, and a standard deviation of 2.84 cm⁻¹. On the other hand, it is lower in the heated samples, ranging from 4.83 to 14.97 cm⁻¹ with an average of 7.23 cm⁻¹, median of 7.06 cm⁻¹, and standard deviation of 1.63 cm⁻¹. In our unheated samples, the FWHM was rarely below 7 cm⁻¹. In our heated samples, the FWHM was rarely above 12 cm⁻¹ but mostly below 8 cm⁻¹, with a variation restricted to less than 3 cm⁻¹ in the same sample. The present work will hopefully further contribute to more accurately identifying the low-temperature heat treatment of pink sapphires from Ilakaka, Madagascar.

gems, corundum, history.1, sapphire, spinel, garnet, beryl, emerald, amethyst, chalcedony

The Imperial Crown of the Holy Roman Empire is not only a unique and outstanding symbol of European history, it is also one of the most significant works of Western goldsmiths’ art from the High Middle Ages. However, little is known about the gem materials it contains. As part of an interdisciplinary research project led by the Kunsthistorisches Museum Vienna in Austria, the 172 gemstones in the crown were all conclusively identified for the first time using (non-destructive) photoluminescence and Raman spectroscopy. They include 71 blue sapphires, 50 garnets (22 almandines, 22 pyrope-almandines, five pyropes and one grossular), 20 emeralds, 13 amethysts, four chalcedonies and three spinels. In addition, 11 glass imitations of various colours were identified. Raman spectral details and inclusions in the garnets support their assignment to garnet types previously found to be used in antique and early medieval jewellery. The large red spinel in the centre of the crown’s front plate is presumably part of the original crown and, thus, is one of the earliest-known spinels in a historic object, yet it yielded spectroscopic evidence of having been heated.

gems, beryl, emerald, Austria, Habachtal

A pectoral cross with nine emeralds and a ring containing one emerald were donated in 1786 to newly elected Abbot Dominikus Hagenauer of St Peter’s Abbey, Salzburg, Austria. Both jewels were examined by microscopy and with a portable X-ray fluorescence unit. The emeralds’ inclusion patterns and chemical properties indicate they are of Colombian origin, although oral tradition has assumed they came from Austria’s Habachtal deposit. The faceting style of the accompanying diamonds indicates that the ring might be somewhat older than the pectoral cross.

gems, beryl, emerald, Pakistan, Swat, Chitral

Michelou and colleagues review the emerald deposits of Pakistan, concentrating on the principal occurrences of the Swat Valley in Khyber Pakhtunkhwa and placing them within their regional geological setting. The chapter describes the geology and mineralization of the deposits, the occurrence of emerald in altered and structurally controlled host rocks, and the characteristics of the crystals produced. It discusses the history of discovery and exploitation, mining methods, production, and the organization of the local trade, together with the practical difficulties posed by the mountainous terrain. The authors also consider the gemological characteristics and quality of Pakistani emeralds, including their color, clarity, inclusions, and comparison with emeralds from other major sources. Additional Pakistani occurrences are reviewed, providing an overview of the country’s emerald resources and their significance within the international emerald trade.

gems, jade, jadeite, fei cui, Guatemala jadeite, fei cui, imperial jade

High-grade green jadeite jade samples from Guatemala were selected as the research objects. Gem microscope, polarizing microscope, microscopic laser Raman spectrometer, and electron probe microanalyser were used to analyze the appearance characteristics, magnification features, constituent minerals, microstructures, Raman spectra, and mineral chemical compositions of the samples. Based on constituent minerals and their evolution, three periods of mineralization were observed. The product of the early mineralization period is jadeite with coarse-grained, hypautomorphic–automorphic granular-columnar texture and very pure chemical composition. The main mineralization period is characterized by metasomatism, with earlier-stage products being fine-grained jadeite containing relatively higher FeO, Cr₂O₃, MgO, and CaO contents compared to jadeite from the early period, and later-stage products being fine-grained omphacite with high MgO and CaO contents, whose green color shades correspond to Cr₂O₃ variation. The late mineralization period products consist of jadeite (or albite) + titanite in a filling texture, with titanite mainly distributed in reticulated veins between jadeite/omphacite particles or in microfractures. The combination of jadeite (or albite) + titanite + fluid inclusions formed during this late stage appears as white cotton-like zones in jadeite jade, representing fluid-melt inclusions. The fluid phase in these inclusions contains CO₂ and CO, with a strong characteristic Raman shift peak at 2,145 cm⁻¹, indicating a highly reductive formation environment with high CO content, corroborated by the presence of amorphous carbon in the samples. Jadeite is the main or one of the main minerals in most of the high-grade Guatemalan green jadeite jade samples studied. In such samples, the late-stage assemblage of jadeite + reticulated titanite + CO-dominated fluid inclusions commonly found in white “cotton” areas serves as an important reference feature for distinguishing Guatemalan high-grade green jadeite jades from Burmese green jadeite jades.

gems, beryl, emerald, Afghanistan, Brazil, Colombia, China, Zimbabwe, Pakistan, Zambia, Madagascar, Mozambique, inclusions, history

This substantial collective volume, edited by Gaston Giuliani, provides a wide-ranging multidisciplinary survey of emerald, bringing together contributions by specialists in geology, mineralogy, gemology, history, archaeology, mining, and the gem trade. It examines the mineralogical and gemological properties of emerald, the geological processes responsible for its formation, and a typology of emerald deposits, followed by detailed treatments of important producing regions around the world, including Colombia, Brazil, Zambia, Zimbabwe, Madagascar, Ethiopia, Pakistan, Afghanistan, and other localities. Individual chapters address the geology and genesis of deposits, exploration and mining, inclusions, chemistry, geographic origin determination, treatments, and other aspects of gemological identification. Historical sections trace the exploitation, trade, and cultural significance of emerald from antiquity to modern times, including Egyptian, European, Islamic, Asian, and American contexts. Richly illustrated with emerald crystals, cut stones, mines, geological features, inclusions, historical objects, and jewelry, the book combines scientific research with the broader human history of one of the world’s most important colored gemstones.

gems, beryl, emerald, Egypt, inclusions

gems, corundum, Madagascar.12, Ilakaka, sapphire

The inclusions and spectral characteristics of blue and orange sapphire from Ilakaka, Madagascar have been studied by Raman spectroscopy, infrared spectroscopy, LA-ICP-MS, UV-Vis-NIR absorption spectroscopy and fluorescence spectroscopy. This study aimed to enrich the information of characteristics of sapphire from Ilakaka, Madagascar. The results showed that the characteristic inclusions of sapphire from Ilakaka included a large number of liquid CO₂-filled negative crystals and healed fissures filled with pseudosecondary inclusions such as goethite and sulfur. It also contained a variety of solid inclusions, such as calcite, graphite, phlogopite, rutile, hematite and kaolinite. The content of Fe in sapphire was positively correlated with the intensity of blue tone. The absorption lines at 377, 387 nm and 451 nm associated with Fe³⁺ were found in all types of sapphire, and the increase of Fe content could promote the formation of Fe³⁺–Fe³⁺ exchange-coupled ion pairs and enhance the absorption at 377 nm and 451 nm. R1 (694 nm) and R2 (693 nm) fluorescence lines of Cr³⁺ were observed in the fluorescence spectra of almost all samples. Orange sapphires had wide fluorescence peaks at 400–480 nm. The low temperature annealing experiment showed that these fluorescence peaks had poor thermal stability and tended to disappear when heated to 250 °C, while the fluorescence peaks increased significantly when heated to 300 °C. The thermo behavior of those fluorescence peaks may be associated with hole centers [V_Al⁺ + O⁻] and [Mg²⁺ + O⁻].

gems, spinel, Afghanistan, Vietnam

This study compares two purple gem spinel samples with regard to trace element chemistry and visible light absorption spectra, and presents the first reported example of a spinel with a saturated purple color caused predominantly by chromium and cobalt. Sample VN, from a placer deposit in the Luc Yen district of Vietnam, exhibited strong saturation, orange-red fluorescence in UV, and magnesite and graphite inclusions. Sample AF was from Badakhshan, Afghanistan, with light to medium saturation and containing phlogopite, amphibole, and probable fluid inclusions. UV-Vis-NIR spectra are compared along with trace element chemistry. Sample VN is colored primarily by cobalt (17.9 ppma) and chromium (593 ppma), with minor color contribution from Fe (2437 ppma), and contains significantly more cobalt than typical Cr-enriched red, pink, and purple gem spinels (<6 ppma Co). The dominant contributions of chromophores Cr³⁺ and Co²⁺ to the color of sample VN are responsible for its higher color saturation than that of sample AF, which is colored dominantly by Fe²⁺ and Fe³⁺ (3089 ppma total Fe) and contains negligible concentrations of other chromophores (<10 ppma V³⁺, Cr³⁺, and Co²⁺). In the Vietnamese purple spinel, the relatively low Fe concentration is likely crucial in creating the attractive saturated color. This sample is enriched in Co, Ni, Cr, V, Zn, and Ga. In contrast, the purple spinel from Afghanistan is relatively impoverished in all trace elements except Fe and Mn. Sample VN represents an approximate intermediate between natural gem spinel populations colored dominantly by Cr³⁺ vs. dominantly by Co²⁺. Cr³⁺-, (Fe²⁺, Fe³⁺)-, and Co²⁺-dominant (in terms of color) gem spinels are easily differentiated by chemical composition using a discrimination plot of Co/Cr vs. Co/Fe, but this is not valid for spinel dominantly colored by V³⁺ or containing significant concentrations of Fe.