Agates are a fascinating and beautiful form of cryptocrystalline quartz and are very popular with gem and mineral collectors and indeed with the general public. This book is aimed at this popular market and is lavishly illustrated, but also contains something for the professional interested in the formation of silica. The volume gives an introduction to agates and then covers the major collecting regions with some emphasis on deposits in Britain and the United States of America.
The volume starts with a very brief introduction and a section on nomenclature that covers a plethora of variety and trade names applied to agates. Agate itself is of course merely a variety name for banded cryptocrystalline quartz. In the section entitled ‘What is an agate?’ Roger Pabian and his co-authors try to explain in simple terms the formation of agate. This is a complex subject and many aspects remain unresolved. What is clear is that agates crystallize from a gel and generally crystallization occurs a low temperature of 40 to 50 °C. The general process of formation of the banding is well explained by a set of excellent schematic diagrams. This section is followed by an illustrated guide to the different types of agate with some beautiful examples, including a photograph of an iris agate, a type of agate in which the banding is so fine and regular that the microstructure acts as an optical diffraction grating. The remainder of the book is largely devoted to information about the localities of agate deposits. Again this section is illustrated with some excellent specimens.
My only reservation is the inclusion of photographs of samples for which there are no locality data. The lack of accurate locality data for samples is the bane of museum curators’ lives. A sample without accurate locality data is largely worthless and it sets a bad example for collectors to include photographs of material without proper data.
Overall this is a nice little book, the design and layout is excellent, and although aimed at the popular market, the authors are to be congratulated for including a fairly extensive bibliography. I am sure that this book with be popular with collectors and the general public.
