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Opal - The Phenomenal Gemstone

The Mineralogical Record

Opal, The Phenomenal Gemstone
by Edited by J. Clifford, P. Clifford, S. Frazier, A. Frazier, B.P. Gaber, C.G. Gaber, G. Neumeier, and G. Staebler

Here is that Look again, as described in the review of Fluorite above: the stiff-cover, elegant, color-on-blackness appearance, this time of Opal: The Phenomenal Gemstone, No. 10 in the ExtraLapis English series, published just a few months after No. 9.

Opal places its major emphasis on rare “precious” opal as opposed to the common “potch” variety. Opal is actually a mineraloid, defined as an inorganic natural substance with uniform chemical composition but no internal crystal structure; “potch” is a synonym for “common,” with connotations of “valueless.” Discussions of opal quite often veer into definitions and sub-definitions and qualifications of terms, and much jargon rooted in opal’s charisma and voluminous lore. Thus it’s helpful that midway through this work we come on “An Opal Glossary of Terms,” compiled by Si and Ann Frazier, to which we can turn when other chapters invoke terms like Ariki, black nobby, cacholong, conk, girasol, hyalite, Newton’s rings, tabasheer, Yowah nut, and many others just as peculiar. Opal seems an especially apt theme for ExtraLapis English, given the series’ habitual practice of mixing accounts of pertinent science, locality data, and other “straight” subtopics with more offbeat aspects of the subject matter.

The non-locality chapters include “Sparkling Opal in Ancient Bones,” about a nearly complete opalized skeleton of a Cretaceous pliosaur (dubbed “Eric”) unearthed in 1976 in Coober Pedy, Australia (Alex Ritchie); an informal narrative of a black-opal mining venture at Virgin Valley, Nevada in the early 1970’s (Paul Clifford); a learned chapter on how synthetic opal is made, with a digression on “photonic opal” and the possibility of “a completely optical, opal-driven computer” in which opal would be to the photon what the silicon chip is to the electron (Michael O’Donoghue); and a look at “Kirschweiler, Germany: an Historic Opal Cutting Center” and once the richest town in Rheinland-Pfalz, if not in all Germany, courtesy of imports of the magical gem from Australia (Klaus Eberhard Wild).

The locality-descriptive chapters are heavy, naturally, on Australia, with separate essays covering White Cliffs, Lightning Ridge, and the protean opal fields of Queensland and of South Australia. Slovakian, Mexican, Brazilian and Honduran opal rate separate chapters each, and then there is “Opal in the United States and Canada” (Catherine J. Gaber) and “Ethiopia to Indonesia: a Sampling of Lesser-known Opal Localities” (Gloria Staebler, Günther Neumeier and the rest of the editorial team).

A chapter by Max Weibel makes very clear how the advent of electron microscopy in the 1960’s and 1970’s enabled an understanding, at last, of opal’s fine structure, and of how the beautiful play of colors in “precious” opal depends delicately on the uniform stacking of tiny silica spheres of uniform size. This discussion completes the one begun by the excellent introductory chapter on “The Opal Enigma: Science, History and Lore” (Si and Ann Frazier).

For gem cutters there are two chapters (respectively by Karl Fischer and Michael O’Donoghue) on how this most sensitive of all gem substances is polished, mounted and protected. For those who worry about the destructive crazing that happens when opal with high water content begins to dehydrate there is “Buying and Caring for Opal” (Bill Cook, Catherine J. Gaber and Janet Clifford). The whole work is bookended by a world map showing notable opal localities and, at the end, the usual multilingual Reference list, this one showing 78 titles.

What can I say that’s sufficiently positive but that I haven’t yet said in reviews of entries in this exceptional series of monographs? “Get one now” is hardly original, but, I suppose, will have to do.

-Thomas P. Moore

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