Book Review Gems & Gemology, Summer 2015, Vol. 51, No. 2

Books: Geology of Gem Deposits, Second Edition

Tara Allen

Books: Geology of Gem Deposits, Second Edition
By L.A. Groat (ed.), 405 pp., paperback, illus., publ. by The Mineralogical Association of Canada, 2014, US$60.00.
This edition of Geology of Gem Deposits, compiled by the Mineralogical Association of Canada, is a collection of technical papers accompanying the short course of the same name that was originally offered in Canada in 2007 and recently held in February 2014 during the gem shows in Tucson, Arizona. The quality of the papers is on the level of those found in scientific journals, addressing an audience knowledgeable about fundamental geologic principles and how they pertain to gem materials.

Each chapter consists of a fully developed technical paper that covers a specific gem material or topic relevant to the audience. For example, the first chapter, which deals with diamond, investigates crystal morphology based on crystallization conditions, implications of δ13C in relation to crystallization environment, and the effects of geologic setting on growth, nitrogen aggregates, and diamond type, among other topics. The subsequent chapters are no less technical, exploring geologic conditions at crystallization, tectonic emplacement, isotopic data for origin and dating purposes, and geothermobarometric techniques for various gem materials, including corundum, beryl, chrysoberyl, topaz, and jade. Some of the graphics could benefit from updating, but the images are generally well done and complement their respective papers appropriately. Chemical data is collected through a variety of methods, depending on the material being discussed and the purpose for chemical analysis, and uses both basic and very advanced testing techniques. Discussions of geologic setting and principles assume a knowledgeable audience. Consequently, the subject material trends on the more technical side, and is not recommended for the casual gem hobbyist. The content will, however, appeal to the geologist seeking context for these gem minerals.

Straying from the general theme of most of the papers in this collection, which focus on a single gem or narrow group of gems, the final chapter is an overview of gem materials found in Canada. Since this is a Canadian publication, this is a fitting end to the collection. “Coloured Gemstones from Canada” is divided by gemstone and then subdivided by locality. Field reports from some of these localities would be an interesting addition to a future edition. Otherwise, the papers are of generally good quality and appropriate to the title of the collection. For the geologically minded, this is a useful compilation of technical papers covering a wide variety of gem materials.

Tara Allen is a staff gemologist in the identification department at GIA’s laboratory in Carlsbad, California.