gems, olivine, peridot, chrysolite, antique jewelry, Baroque jewelry

Examines the origin of the large peridots used in European Baroque jewellery during the later seventeenth and early eighteenth centuries. In the author’s earlier conference account, microscopic examination of treasury objects, particularly a jewel box made in Augsburg around 1670 and preserved in St Vitus Cathedral, Prague, revealed inclusions arranged along successive crystal-growth zones. These strongly favour Zabargad Island in the Red Sea over the basalt-associated deposits at Kozákov in Bohemia. Hyršl suggests that renewed, possibly short-lived exploitation of Zabargad supplied central Europe during the seventeenth century. Relevant to historical gemstone provenance and trade.

corundum, Geology.11, Madagascar.12, gems

Madagascar is one of the principal producers of gem corundums recovered from continental basaltic fields. The main deposits are the secondary deposits of Ambondromifehy from the Antsiranana Province in the northern part of the country (sapphire-bearing palaeoplacer and placer), Soamiakatra–Mandrosohasina from the Antananarivo Province in the central part (primary ruby deposit, and ruby and/or sapphire-bearing placer and palaeoplacer), and Vatomandry from the Toamasina Province in the eastern part of the island (ruby- and sapphire-bearing paleoplacer). Soamiakatra is the only known primary deposit where ruby is found in metagabbro and pyroxenite xenoliths, which were entrained and brought up to the upper crust by the Ankaratra volcanic event. Petrographic studies have demonstrated the existence of two different conditions of ruby formation at the boundary of the eclogite domain (HT ~1100 °C, HP ~20 kbar) and granulite facies (HT ~1100 °C, BP <15 kbar). In contrast, the sapphires originated from alkaline mafic magmatic chambers at the lower continental crust–mantle boundary. They occur within syenite and anorthoclasite xenoliths in the basalts or are associated with them. These alkali basalts transported corundum and their host rocks to the surface; they are linked with asthenosphere upwelling and thinning of the lithosphere underneath the Ankaratra Plateau during the Oligocene–Quaternary. The mineralogical study of ruby and sapphire permitted us to establish the relationships that exist between their chemical composition, their colour, and the nature of their solid inclusions. Iron is the main chromophore of sapphire, and the Fe²⁺/Fe³⁺ ratio in its structure, in addition to the quantity of titanium and chromium available in the fluid, determines the colour of the sapphire and the hue of the polychrome sapphires. Chromium is the second most important chromophore for pink, violet-blue, and some blue-green to light-blue sapphires. For ruby, chromium is the chromophore, but iron and vanadium interfere to produce red-brown to purplish-blue crystals. The deeply coloured, high-quality rubies are characterized by a Fe₂O₃/Cr₂O₃ ratio less than 1. The chemical diagrams used for the genetic classification of corundum indicate a metamorphic origin for all rubies from the central and eastern regions of Madagascar: rubies are hosted either by mafic and/or ultramafic rocks or by metasomatites formed by fluid–mafic rock alteration (“plumasite” or biotitite). Two processes have been identified to explain the origin of sapphires from the different regions: (i) a dominant magmatic process linked to syenites (anorthoclasite), and (ii) a metamorphic process (probably of skarn type). The oxygen isotopic compositions of the corundum corroborate these two origins. Solid inclusions such as pyrochlore, samarskite, uraninite, and anorthoclase in the sapphires confirm their syenitic origin. The presence of pentlandite, talc, sillimanite, titanite, and phlogopite in the rubies testifies to a metamorphic paragenesis.

corundum, Mozambique.12, gems

Rubies have recently been discovered in northern Mozambique, specifically in Niassa Province (M’sawize village, Lichinga district) and Cabo Delgado Province (Montepuez area). These rubies display internal features such as twin planes, fluid-film inclusions, negative crystals, and crystalline inclusions. Many of the crystalline inclusions are colorless to green amphibole (possibly pargasite), along with confirmed apatite and fine needles producing “silk.” Some fractures contain material resembling hematite. Infrared spectra of unheated Mozambique rubies show a broad absorption band at 3309 and 3081 cm⁻¹, which disappears after heating; weak bands at 2074 and 1980 cm⁻¹, likely from diaspore, may also be present. EDXRF analysis reveals Cr contents of 0.3–0.8 wt.% and Fe contents of 0.2–0.5 wt.%, higher than typical non-basalt-related rubies but lower than basaltic rubies. Most Mozambique rubies have been heat-treated, often leaving flux residues in fissures.

corundum, USA.12, Montana, Russia.12, oxygen isotopes - corundum - sapphire - Yogo-Gulch - Tunkin depression - Podgelbanochnyi volcano - Russia - United States, gems

Abstract This paper reports an oxygen isotopic study of corundums and associated minerals from the Yogo lamprophyres (Montana, US), plagioclase-corundum inclusions in alkali basalt (Tunkin depression, Russia), and from modern alluvium of Podgelbanochnyi alkaline basaltic volcano (Primorye, Russia). It is shown that all sapphires genetically related to mafic magmatic rocks have a similar oxygen isotopic composition (the variations of δ18O are within 2.5‰) with most values plotting between +4.5 and +7.0‰ SMOW. The oxygen isotopic ratios in the associated minerals (olivines, pyroxenes, mica, and others) and host rocks are plotted in the same interval. This indicates that the sapphire crystallized during evolution of the parental mafic magma. However, there are xenogenic corundums, which were only transported by basaltic magma to the Earth’s surface. They have a sharply distinct oxygen isotopic composition, which suggests their disequilibrium with the host lavas, and, correspondingly, a different genetic nature.

corundum, treatments.6, gems

This research update examines beryllium in blue sapphires and its implications for identifying diffusion treatment. Analyses of 28 sapphires collected at Ilakaka, Madagascar, detected naturally occurring beryllium in 12 samples, with local concentrations of 1–20 ppm. Independent laboratory analyses confirmed the findings. Beryllium appeared concentrated in comet-tail inclusions associated with niobium, tungsten, tin, and tantalum. These associations suggested a possible means of distinguishing natural beryllium from artificially diffused material, demonstrating that beryllium detection alone does not establish treatment.

gems, bery, beryl, emerald, inclusions, Afghanistan, Panjshir

corundum, color.4, treatments.6, gems

An investigation of the high-temperature beryllium diffusion treatment used to produce yellow, orange, and pinkish-orange colours in sapphire. Chemical analyses demonstrate that externally introduced beryllium penetrates the stones and correlates with the altered colour zones. The article describes diagnostic clues, including orange rims around pink cores, strong yellow-orange fluorescence, and heat-altered inclusions, while explaining the role of SIMS and laser-ablation ICP-MS in detecting low beryllium concentrations. It also reviews the treatment’s emergence, proposed colour mechanisms, and controversies surrounding identification, nomenclature, and disclosure.

corundum, geology.11, gems

This doctoral thesis investigates the origin of marble-hosted ruby deposits across Central and Southeast Asia through petrography, geochemistry, geochronology, fluid inclusions, and isotopic analysis. It links mineralization to Himalayan metamorphism following collision of the Indian and Eurasian plates. The proposed model derives aluminium and colouring elements from impurities within carbonate sediments, with evaporitic salts facilitating their mobilization. Isotopic evidence supports predominantly internal metamorphic fluids and largely closed-system formation, rather than substantial input from neighbouring magmatic rocks.

corundum, geology.11, inclusions.5, Myanmar (Burma).12, trapiche ruby, gems

After a comparison of the geologic occurrences of trapiche emerald and trapiche ruby, and a discussion of the various theories proposed for their formation, this article presents the results of an investigation of the chemical compositions, and the solid and fluid inclusions, of six trapiche rubies from Mong Hsu. The study used advanced analytical techniques such as energy- and wavelength-dispersive spectrometry and “cold” cathodoluminescence. The authors identify 12 minerals not previously reported as inclusions in trapiche rubies or as components of their skeletal “arms.” The rubies show a chemical zonation that can be linked to variations in the chemical composition of the growth fluid. The chromium content, in particular, appears to be related to variations in the circulation of metasomatic fluids rich in REE (rare-earth element) fluorides.

gems, garnet, andradite, demantoid, Pakistan

Reports on 50 faceted demantoid garnets reportedly originating from a peridot mine in the Pakistani part of Kashmir. The stones range from yellowish green to emerald green and weigh 1.04–11.38 ct, with specific gravities of 3.77–3.85. Chemical analysis identifies relatively pure andradite containing approximately 0.25 wt.% chromium oxide. Needlelike, fibrous, and felted mineral inclusions are identified as chrysotile, documenting their occurrence in Pakistani demantoid.