corundum, synthetic corundum.7, gems

Sapphire (Al₂O₃) single crystals were grown using the Czochralski technique in both air and argon atmospheres, with growth conditions calculated through Reynolds and Grashof numbers; a critical crystal diameter of 20 mm and a critical rotation rate of 20 rpm were determined from melt hydrodynamics, while the experimentally established growth rate was 3.5 mm/h; chemical polishing was effectively achieved with concentrated H₃PO₄ at 593 K for three hours, and etching at 523 K for the same duration proved suitable; X-ray powder diffraction gave lattice parameters of a = 0.47573 nm and c = 1.29893 nm, and the results were discussed in comparison with existing literature.

corundum, color.4, treatments.6, gems

gems, gem trade in Asia, gem business, trade between Europe and Asia, diamonds, rubies, pearls, corundum, Persia, Chardin

corundum, color.4, treatments.6, gems

The Defect Chemistry of Metal Oxides is a unique introduction to the equilibrium chemistry of solid inorganic compounds with a focus on metal oxides. Accessible to students with little or no background in defect chemistry, it explains how to apply basic principles and interpret the related behavior of materials. Topics discussed include lattice and electronic defects, doping effects, nonstoichiometry, and mass and charge transport. The text distinctly emphasizes the correlation between the general chemical properties of the constituent elements and the defect chemistry and transport properties of their compounds. It covers the types of defects formed, the effects of dopants, the amount and direction of nonstoichiometry, the depths of acceptor and donor levels, and more. Concluding chapters present up-to-date and detailed analyses of three titanium dioxide, cobalt oxide and nickel oxide, and barium titanate. The Defect Chemistry of Metal Oxides is the only book of its kind that incorporates sample problems for students to solve. Suitable for a variety of courses in materials science and engineering, chemistry, and geochemistry, it also serves as a valuable reference for researchers and instructors.

corundum, Laos.12, gems

This saphire deposit is occurred in the Holocene alluvium. The saphire is characterized by blue colour, coarse grain, good transparency, less flaw and easy processing. Its quality is higher by one grade than that in China. And it is possible to find out the saphire with grade A in this ore-field.

gems, corundum, chemistry.2, crystallography

This volume offers a comprehensive crystallogenetic overview on the morphology of minerals based on the authors' original ideas. Theories of crystal growth are briefly dealt with, attenetion being paid to the classical layer-by-layer and dislocation mechanisms. The modification of crystal forms of the most important rock-forming and ore-forming minerals, presented by their principal crystal habits, is checked by both observation in their natural occurences and laboratory experiments. Crystal growth by accretion of clusters and/or submicroscopic crystallites under specific natural environments is also discussed. The examples used illustrate crystallization and variation in the crystal habits of minerals in magnetic, pegmatitic, hydrothermal, weathering, sedimentary and metamorphic environments. The trends of crystal habit variation have been used for genetic interpretations and for outlining corresponding morphological zonalities.

corundum, geology.11, Tajikistan.12, gems

Corundum-bearing rocks containing ruby, sapphire, and pink sapphire are found in the Kukurt gemstone field, in the Pamir Mountains of southern Tajikistan. The authors used rare-earth-element (REE) data and other geochemical characteristics of rocks in this region to study the processes and conditions of corundum formation. This research, and related work by other scientists, suggests that the oldest rocks in the Kukurt area under-went a major metamorphic event more than 500 million years (m.y.) ago. Corundum mineralization occurred. much more recently, about 20 m.y. ago, during the formation of the Himalayas. Most of the corundum occurrences are related to linear geologic structures such as shear zones and lithologic contacts; they are found in several different rock types, mainly marble and gneiss. According to the authors, geochemical enrichments in REE, Al, Ti, and several trace elements—as well as the association of minerals rich in Cl, B, and F in the corundum-bearing rocks—suggest that gem corundum mineralization was caused by through-flowing volatile-rich fluids that possibly originated in a deep-seated mantle source. Fluid movement was facilitated by the active deformation associated with mountain-building events. Since these events were regional in character, other commercially viable corundum deposits may be found through the application of these models to geologically similar areas in the high mountain ranges of Central Asia. JL

corundum, sources.12, Thailand.12, Bo Ploi, inclusions.5, gems

Three main types of fluid inclusions occur in Bo Ploi sapphires: (1) vapor-rich CO₂ with a density up to about 0.86 g/cm³; (2) multiphase inclusions containing several daughter minerals, hypersaline brine, and a CO₂-rich vapor phase; and (3) (silicate?)-melt inclusions with immobile vapor bubbles in an isotropic or weakly anisotropic phase of low relief, with bubbles becoming mobile when heated above 800 °C. These observations suggest a magmatic origin for the sapphires, although they did not crystallize as phenocrysts within the basalts that transported them to the surface.

corundum, sources.12, Tanzania.12, gems

Tanzania emerged as a great producer of colored gemstones in the second half of this century. Most of the important localities (e.g., Longido, Lake Manyara, Merelani, and Umba) are in the northern part of the country; they produce a great variety of gems, the most impor-tant being tanzanite, corundum (ruby and fancy-color sapphires), garnet (particularly rhodolite and tsavorite), tourmaline, emerald, alexandrite, spinel, and quartz. Diamonds are mined from the Mwadui kimberlite pipe, also in the north. Historically, gemstone occurrences in the south have been rare.. In 1994, however, large and rich gem deposits were found in southern Tanzania in the vicinity of Tunduru, about 80 km north of the border with Mozambique. An estimated 80,000 “illegals” have been working the alluvial deposits in the vicinity of the Muhuwesi and Mtetesi Rivers, mostly by primitive methods. Although the primary sources of the gem minerals have not been found, the fact that some crystals are only slightly rounded indicates short transport distances. This article discusses the history of the discovery and the development of gemstone trade in this area, the geologic setting of the deposits (in the Proterozoic Ubendian-Usagaran System of metamorphic rocks), and the most important gem materials found to date. These include blue and fancy-color sapphires, ruby, many colors of spinel, garnet (rhodolite, hessonite, and color-change), and chrysoberyl (cat’s-eye and alexandrite).PB

corundum, synthetic corundum.7, gems

Gemological investigations of Tairus hydrothermal synthetic ruby revealed characteristic microscopic features, including solid alloy inclusions consisting mainly of copper–iron alloys and wavy growth lines. Chemical analysis by microprobe showed that the chromium concentration in the area of the growth lines averaged 3.81 wt.% Cr₂O₃, as compared to 1.53 wt.% Cr₂O₃ in the remainder of the stone. Characteristic infrared absorption peaks are 3308, 3233, and 3186 cm⁻¹.