A very rare gem-quality crystal of hurlbutite, CaBe2(PO4)2, was recently examined and subsequently faceted into two gemstones. The near-colourless 17-mm-long prismatic crystal was of exceptional size for this species, which typically occurs as translucent masses or crusts. It was faceted into two gems weighing 0.64 and 2.56 ct. The gemmological, chemical, spectroscopic and crystallographic characteristics of the samples are in close agreement with the limited published reference data for hurlbutite. Our spectroscopic examinations revealed hydroxyl-related FTIR absorption bands, as well as luminescence features that may be due to manganese and trivalent rare-earth elements. To the authors' knowledge, this study documents the largest-known example of faceted hurlbutite, and provides the first description of this material as a gemstone.
Minor-and trace-element data constitute a chemical 'fingerprint' of the geological environment of gem mineral formation and, hence, the possibility of determining geographic origin when used in combination with other observations. We evaluated the common practice of using LA-ICP-MS analysis to acquire multiple spot analyses of a gemstone (typically from the girdle surface), and whether three or more such analytical spots are sufficiently representative of a gem's overall chemical composition. For this study, we selected a blue sapphire from Ilakaka, Madagascar, showing significant compositional diversity due to zones with low-and high-density micro-inclusion clouds. We obtained 3,000 LA-ICP-MS analyses from an area of the sapphire encompassing both cloud-poor and cloud-rich zones. K-means cluster analysis suggested that analysing more than three spots appears to provide a diminishing improvement in overall analysis accuracy. Statistical analysis of the data showed that the median (rather than the mean) composition of the analytical spots may provide a balanced evaluation of a stone's composition, complementary to considering multiple single-spot analyses. Although this evaluation used a single corundum sample, it provides a framework for understanding how other gem materials can be statistically characterised at the trace-element level.
This study investigates the mineral composition, causes of colour, and formation process of bright green, deep green and 'black' jadeite jade and omphacite jade from Kazakhstan by applying a combination of infrared and UV-Vis-NIR spectroscopy, EDXRF chemical analysis, Raman spectroscopy and Raman mapping. The deep green samples were mainly omphacite and were relatively homogeneous in composition. The bright green and black specimens were primarily jadeite. In the bright green and deep green material, Cr was the principal colouring element, and the presence of Fe caused a darker tone. By contrast, the dark colour of the black jadeite was caused by particulates of graphite. White areas within the bright green specimens contained significant amounts of analcime. Based on the relationship between analcime and jadeite and the pressure-temperature conditions of formation, we infer that this type of Kazakhstan jadeitite formed in at least two stages.
An emerald from the late Hellenistic (or early Roman) period and another emerald from the end of the Middle Ages, both set in small rings, were studied using non-destructive methods. Their microscopic, spectroscopic and chemical characteristics are consistent with those of emeralds from the Swat Valley, Pakistan. This suggests that Swat Valley emeralds may have been more common in ancient jewellery than previously thought. This study highlights the importance of combining gemmological analytical techniques with archaeology to draw more reliable conclusions about the origins of historical gemstones.
This study examines sapphires naturally enriched in high-field-strength elements (HFSE) from metamorphic origins in Sri Lanka and Madagascar. These sapphires display distinctive chemical inhomogeneities and microscopic growth features, as well as variable FTIR spectra, often including a broad absorption band near 3300 cm-1. Some of the studied samples also show FTIR spectral characteristics and short-wave UV luminescence typically associated with heat-treated stones, although all were unheated. Our findings demonstrate that commonly used indicators-such as specific FTIR band patterns (mainly the 3309 cm-1 triplet) and chalky bluish white short-wave UV fluorescence-are not always reliable for identifying heat treatment. Accurate distinction between heated and unheated sapphires requires detailed microscopic examination combined with advanced trace-element analysis and spectroscopic techniques, including Raman micro-spectroscopy of inclusions such as zircon, goethite and diaspore.
