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Tourmaline-Fascinating Crystals with Fantastic Inner Worlds.

Tourmaline-Fascinating Crystals with Fantastic Inner Worlds By Paul Rustemeyer, 2015. Verlag Dr. Friedrich Pfeil, Munich, Germany, 272 pages, illus., ISBN 978-3899371949, www.pfeil-verlag. de/06geol/e4_94.php (in English and German). 59.80 [euro] hardcover.

In the preface of this impressive book, the author states: "The observer might become meditatively immersed in the tourmaline paintings and may go on imaginative trips into the new landscapes." Indeed the photographs in this book (many of which resemble beautiful paintings) certainly transport the reader to another world--the colourful patterns seen in slices of tourmaline.

The book is printed on high-quality paper, is beautifully designed and laid-out, and the reproduction quality of the photos is excellent. Many of the tourmaline crystals are shown before they were sliced and are accompanied by photographs of the resulting slices (or series of slices). Selected full-page enlargements of some of the more spectacular portions of the slices further reveal amazing colours and patterns that would mostly go unseen without magnification. A black background is used on every page not containing a full-page photo, allowing the images to truly 'pop'. The limited amount of text (always appearing on left-hand pages) is well written and easy to understand for non-specialists. Different font colours are used for English (yellow) and German (white), making it easy for the reader to find their preferred language.

The author has arranged the sections of the book according to the main cause of the dominant patterns shown by the slices:

* 'From Black Crystals to TurmalinArt' presents a series of examples that reveal the inner beauty of black tourmaline crystals when thin sections of them are prepared perpendicular (and in some cases, parallel) to the c-axis. The author explains how he saws the crystals into slices and polishes one side before mounting them on glass slides for final grinding and polishing until the optimal colour appearance is displayed (typically only 0.1-0.01 mm in thickness).

* 'The Structure of Tourmalines' briefly reviews the crystal structure of the mineral to help put the geometric patterns seen in slices into context. Also included are photos of crystal specimens showing myriad variations in colour and morphology.

* 'The Color Palette of the Tourmalines' illustrates the tremendous variety of colours seen in faceted gemstones and in crystals. Simplified explanations of the causes of colour are provided.

* 'The Growth of Tourmaline Crystals' contains many attractive diagrams and photos of tourmaline specimens to illustrate their crystallization process in granitic pegmatites. (Tourmaline formation in metamorphic rocks is not covered.)

* 'The Structures of Crystal Forms' provides an excellent correlation between the various crystal faces and the patterns seen in slices cut perpendicular to the c-axis.

* 'Rim Structures' focuses on features seen within the concentrically zoned portions of slices, which correspond to prism faces.

* 'Oriented Overgrowth' displays the complex mosaic structures seen in slices when a crystal is overgrown by a series of needles and tubes parallel to the c-axis. Also shown are features attributed to skeletal overgrowths.

* 'Delta Structures' portrays a specific type of triangular zoning in tourmaline slices that corresponds to the localized growth of steeper pyramidal faces. The resulting features are particularly reminiscent of landscapes, especially when they are influenced by dislocations in the crystal.

* 'Trigonal Dislocations' provides examples of the complex patterns that result when defects in the lattice of a growing crystal propagate as dislocations.

* 'Division into Parallel Aggregates' shows interesting mosaic networks that result when a growing crystal gradually or abruptly changes into an aggregate structure that is oriented parallel to the c-axis.

* 'The Healing of Broken Tourmalines' records periods of regrowth in 'bent' and broken crystals, including the formation of parallel tubes that may create chatoyancy in cabochons.

* 'Naturally Corroded Tourmaline Crystals' depicts geometrical etch pits and hillocks resulting from post-grown dissolution, beautifully revealed in photomicrographs taken in reflected light.

* 'Healing of Corroded Tourmalines' shows the results of further crystal growth (often by tourmaline of a different colour) after a period of dissolution.

* 'Healed Corrosion of Cavities' displays some particularly abstract patterns that are produced when irregular areas of dissolution that penetrated deep within a crystal are filled-in by subsequent tourmaline growth.

At the conclusion of the book, the author provides a brief bibliography of tourmaline monographs (with a full listing of tourmaline literature supplied at http:// www.pfeil-verlag.de/ef1.html), as well as an index.

While it is easy to become pleasurably absorbed in the richness of the photography, the scientific value of this book should not be overlooked. Through the use of helpful diagrams and photographic comparisons of crystals before and after slicing, as well as neatly arranged series of slices that were obtained from the same crystal, the reader comes away with a much better understanding of the complex crystal growth history of tourmaline.

This reviewer noted only a few very minor errors in the text: p. 42 indicates that the blue colour of Paraiba tourmaline is due to 4% copper, while much lower amounts of Cu are typical (i.e. ~0.5-2 wt.% CuO); p. 44 gives the location of Sweet Home mine rhodochrosite crystals as Utah, rather than Colorado; p. 160 mentions earthquakes as the cause of broken tourmalines that subsequently undergo regrowth in pegmatite pockets, but such breakage is commonly ascribed to pocket rupture due to fluid overpressure; and throughout the book verdelite (green tourmaline) is referred to as 'verdilithe'. In addition, a table-of-contents page would have been helpful for navigating the book.

It is rare to encounter such an effective and inspirational melding of art and science applying to any mineral. This book is sure to please tourmaline aficionados, and also will appeal to many mineralogists, gemmologists, photographers and those who appreciate the beauty of the natural world.
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Author:Laurs, Brendan M.
Publication:The Journal of Gemmology
Article Type:Book review
Date:Dec 1, 2015
Words:947
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