corundum, color.4, gems

corundum, geology.11, gems

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.

corundum, geology.11, gems

Based on mineralogic and geologic research on corundum occurrences in Russia, and published data on corundum localities occurring elsewhere, it is emphasized that regional metamorphism of different rock types (e.g., marble, gneiss) is the major factor controlling the formation of corundum deposits and determining the quality of the gems they contain. The chemical and physical properties of the metamorphic host rocks ultimately determine the characteristics of gem corundum. The sapphires from Kashmir and rubies from Myanmar, which formed in metamorphic environments, are cited as examples. The superb gems from these deposits had the appropriate chromophoric elements available during their formation, under the proper metamorphic conditions. Characteristic mineral inclusions are considered indicative of specific genetic types of corundum, and, for alluvial stones, the inclusions can be used to infer the origin of the gem corundum. Gem corundums originating from other geologic sources (e.g., igneous or metasomatic) are likely to be of lower quality than those of metamorphic origin.

corundum, treatments.6, padparadscha,, gems

Since 2001, large amounts of treated orange to yellow and “padparadscha”-like sapphires have appeared in the gem trade. The rough material mainly came from Songea (Tanzania) and Ilakaka (Madagascar). About 150 of these stones were examined with several methods. The results showed that the stones were not only heat treated, but also diffusion-treated with beryllium (Be). The diffusioninduced color may extend as much as several millimeters into the stone (which, when small, means the entire stone). Unlike traditional diffusion treatment, the Be diffusion may not be undetectable by viewing the color distribution in immersion.. The Be content in corundum is normally less than ~1 ppm. However, this new Be diffused corundum typically contains 10–15 ppm beryllium. The original trace-element contents of the natural material strongly influence the outcome of the diffusion treatment. This new type of diffusion-treated sapphire has raised concerns about the identification of such stones and the terminology used to describe them.

corundum, synthetic corundum.7, gems

The Stepanov method is a specialized technique for growing crystals from a melt. Compared to other melt processes, such as the Czochralski or “pulling” method, its major advantage is that the shape (cross-section) of a crystal can be gradually changed during growth. The basic requirement is that a melt column with a defined shape be formed, which is accomplished with the aid of a special “shaper.” Liquid melt columns with various shapes can be made by properly applying a high-frequency electromagnetic field.. Since the initial work by Stepanov in 1938, progress in developing the method has proceeded along two lines: (1) development of technology for producing single crystals of a desired shape, and (2) understanding the physical phenomena involved in the formation of the shaped crystals. Synthetic sapphire crystals with various defined shapes, primarily for industrial use, have been successfully grown using this technique. For example, synthetic sapphire tubes up to 85 mm in diameter and ribbons 120 mm wide have been grown and used for their optical properties. Sapphire rods with various shapes have also been grown. Microvoids and gas bubbles are the main defects found in such crystals.TL

corundum, treatments.6, gems

corundum, color.4, quality.10, Sri Lanka.12, gems

gems, corundum, Ceylon.12, Sri Lanka.12

A posthumous collection of Ananda K. Coomaraswamy’s writings on the geology and mineralogy of Ceylon, bringing together his scientific papers, official reports, and related comments from the period when he served as Director of the Mineralogical Survey of Ceylon. The volume documents his geological and mineralogical investigations of the island, including studies of rocks, minerals, ore deposits, and economically important mineral resources, and reprints his Ceylon Administrative Reports for 1903–1906. Of particular gemological interest are his observations on Ceylon’s gem deposits and gem-mining industry, including the occurrence, recovery, and distribution of precious stones. The collection preserves the early scientific work of Coomaraswamy before his subsequent career as an influential historian of Indian and Asian art and provides an important contemporary source for the geology, mineralogy, and gemology of early twentieth-century Ceylon.

gems, Somalia, Somaliland, ruby, sapphire, garnet

Recent geological surveys indicate that Somaliland has abundant deposits of gemstones, from emerald to aquamarine, ruby and sapphire as well as vast amounts of garnet, quartz and opal, and lesser-known minerals such as titanite and vesuvianite. Somaliland in northern Africa appears to be the new potential gemstone-bearing area comparable to Madagascar or Tanzania. In addition to pegmatite, which are the host rocks of emerald and other kinds of beryl such as aquamarine, Somaliland has metamorphic rocks that hold nodules of ruby and sapphire. There is little understanding of its mineral deposits, but villagers in Somaliland use primitive tools to dig out a range of gemstones that they offer for sale to dealers locally. When aid officials at the European Community (EC) office in the capital, Hargeisa, first saw the gemstones, they believed they had been stolen from graves. To determine whether these stones came out of the ground or were stolen, EC invited Dr. Judith Kinnaird, a consultant geologist and gemmologist from the University of Witwatersrand in Johannesburg, to investigate. Dr. Kinnaird visited the country twice and, in addition to identifying gem minerals, she helps local miners distinguish among similar coloured minerals and is working with Progressive Interventions (supported by EC funding) to help set up a gemmological association and marketing channels. Somaliland is part of the Mozambique Belt and was formerly part of the same landmass as Madagascar, Tanzania, Sri Lanka and India prior to continental drift. Recovery of gemstones began only in 1988 and is still carried out in a primitive and haphazard manner. The gem-producing belt is a narrow strip between 30 and 80 km wide and 200 to 300 km long, running roughly parallel to the Gulf of Aden. The country, once a British protectorate, suffered a nine-year civil war from 1982, leaving infrastructure like roads and bridges in disrepair. Dr. Kinnaird described access to gem deposits as difficult and hazardous. The terrain includes high mountains and coastal regions with temperatures reaching up to 50°C. Two emerald-producing areas, Alihiley and Simodi, occur at the contact of pegmatite and chromium-bearing schist. Patchy colour development and dual-colour zoning were observed in crystals. At Simodi, pegmatite is visible across the hillsides, and emerald is being mined again after years of inactivity, despite dangerous pit conditions and lack of equipment. In Alihiley, rudimentary mechanical tools like a compressor are used. East of the emerald belt, aquamarine and other beryls occur in pegmatite intruding granite, giving rise to large but often cracked crystals coloured by iron or titanium. Reports also mention yellow beryl (heliodor). Ruby and sapphire are found in metamorphic rocks, not pegmatite. Ruby has been found in red corundum cores with green zoisite, while sapphire occurs in nodules, greenish-blue near the surface and better-quality blue material at depth. Unlike other African countries, ruby and sapphire are not found together. Garnet is extremely abundant, in red to orange colours and of multiple types, including pyrope and almandine, and some green garnets initially mistaken for Tsavorite were identified as vesuvianite. Orange to yellow opals lacking play-of-colour have been found, but high-quality reddish opal with good play-of-colour also occurs, possibly in both lava and gypsum/anhydrite strata. Quartz is widespread, including high-purity rock crystal, smoky quartz, banded forms, and deep purple amethyst. Additional minerals include red spinel, watermelon tourmaline, colourless topaz, blue and green vesuvianite, titanite, apatite, and zircon. Some locals mistake quartz for diamond, though Dr. Kinnaird clarified there are no diamonds in Somaliland.