corundum, chemistry.2, gems

corundum, quality.10, Burma.12, gems

corundum, treatments.6, gems

corundum, Sri Lanka.12, gems

gems, ruby, sapphire, corundum, Tajikistan.12

Rossovskii gives a brief regional synthesis of ruby and sapphire deposits within the Alpine–Himalayan fold belt, considering their geological settings and conditions of formation. The paper places corundum occurrences within the broader tectonic and metamorphic framework of the belt and compares the principal geological environments in which gem-quality ruby and sapphire occur. Particular emphasis is placed on the relationship between corundum mineralization and metamorphic or metasomatic processes, including ruby occurrences associated with marbles. The contribution is essentially a concise metallogenic overview intended to identify common geological controls on the distribution and genesis of gem corundum across this extensive belt.

corundum, chemistry.2, gems

Harder and Schneider investigate experimentally how cooling rate controls whether Ti-bearing corundum develops asterism or a cornflower-blue color. They relate the two effects to the behavior of titanium during cooling: under conditions permitting exsolution, titanium is precipitated as oriented rutile needles, producing the silk responsible for asterism; under different cooling conditions, titanium remains incorporated in the corundum lattice, where interaction between iron and titanium produces blue coloration. Thus, corundum of essentially comparable composition can develop either the oriented rutile inclusions required for a star effect or the transparent blue appearance characteristic of sapphire, depending upon its thermal history. The paper emphasizes cooling rate as a decisive factor governing the distribution of titanium between the corundum lattice and exsolved rutile.

corundum, color.4, gems

corundum, USA.12, Montana.12, Yogo, Vortex, gems

corundum, geology.11, Australia.12, gems

gems, bibliography, book collecting, books on gems and jewelry, mineralogy

Nigel Israel: This is an extremely useful little book (booklet would, I think, be a better description) by the Curator of Earth Sciences at the British Library. Starting with a general preface and introduction, it attempts, quite successfully, to list the more important works on gemmology under various categories, including encyclopaedic works, general comprehensive surveys, gem testing, gem testing instruments, quick reference publications, textbooks, synthetic gemstones, fashioning, works on individual species, jewellery, gemstones of particular localities, bibliographies, abstracts, journals, gemstone prices, guides to collections, and regalia. The works are listed with their publication details, including if and where they are held by the British Library, and, in many cases, with helpful descriptions by the author. The book ends with a useful index, followed, inexplicably, by two pages of beryl and corundum crystal diagrams. The literature of gemmology is extremely large, so the selection is necessarily a personal one by the author, and many people will likely be surprised by the omission of some of their favorite works. The reviewer was personally most surprised by the exclusion of Diamonds and Precious Stones by Emanuel (1865 and 1867), as this book contains an extremely extensive bibliography of historic books on gemstones. However, despite the unfortunately high price of a soft-covered booklet of little more than photostat quality, I would certainly recommend The Literature of Gemstones (together with the author’s companion work The Literature of Mineralogy) to anyone interested in gemmology.