Rocks and Minerals, Jul/Aug 2005
Pegmatology is a new term coined in recent years by those with an intense, generally uncontrollable interest in pegmatites and their minerals. It is an appropriate term, and the ranks of those devotees (who are obviously called pegmatologists) appear to be growing. It seems, therefore, only appropriate that those addicted to the faint punky odor of weathering feldspar have a handbook, one that can be counted on to answer all conceivable questions, from the basics of how Earth's crust has evolved to the details of minerals essentially unique to pegmatitic environments. Pegmatology fills the bill. It has been clearly written at a level consistent for use by graduate students and advanced amateurs, although there is much therein that many professional mineralogists will likely find new to them.
The book is logically divided into fifteen chapters. It begins with a discussion of exactly what pegmatites are and how they are classified. A chapter on fundamental concepts of plate tectonics, the chemical composition of the crust, minerals in general, and the three rock groups follows. Next are three chapters that deal with the origin of magmas, magmatic differentiation, and plate-tectonic settings related to magma generation. Chapter six brings us to our initial discussion of granites and pegmatites; it is expanded in the following two sections through a presentation of the details of regional and internal zoning, and pocket formation. On page 41 we begin our journey through pegmatite mineralogy. This approximately 90-page chapter is divided into fifteen sections that build from the ubiquitous, abundant minerals such as quartz, the feldspars, and the phyllosilicates, through the more familiar accessory phases such as the tourmalines, garnets, spodumenes, and beryllium minerals, to the rarer minerals of particular interest to collectors such as niobium, tantalum, and other oxides; phosphate minerals; native elements and sulfides; borates; halides; other silicates such as topaz, danburite, and zeolites; and carbonates. The depth of discussion of families, groups, and species is variable, with the greatest attention given to tourmaline-group minerals. The final six chapters deal with more technical issues. These include pocket indicators; volatiles in pegmatites; cooling and crystallization histories of pegmatites including a lucid presentation of the origin of "line rock"; and petrogenetic indicators. The last chapter discusses geophysical and geochemical exploration tools using the economically important, though poorly known to collectors, giant Bernic Lake, Manitoba, pegmatite as an example. There is a comprehensive set of references followed by four appendices that include a nice review of the fundamentals of crystallography, the periodic table of the elements, a listing of elements and their crustal abundances, and the IUGS classification chart for phaneritic nonmafic igneous rocks.
The book is well illustrated with 322 figures, most of which are in color. These range from many photographs of minerals and accompanying crystal drawings to technical diagrams carefully selected and in-part redrawn from classic works on specific aspects of pegmatite geology. Additionally, the text is augmented with numerous tables in which otherwise scattered information has been carefully gathered and presented. The work is well written and edited. The photographs are generally small and of variable though good quality and illustrative of the minerals they represent; a few normally gray to black crystals have a decided blue cast. Pegmatology is a well-done educational work that should be used as a source book by all who endeavor to find or otherwise collect pegmatite minerals, or by those who wish to fine tune their overall knowledge of this fascinating subject. It is highly recommended.
-Robert B. Cook
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