Each gem deposit-whether of primary origin in the parent rocks; or secondary as alluvial placers in valley floors, river gravels, or the sand of oceanic shelves presents an eloquent chronicle of the Earth's life story. It reveals to the expert the prodigious processes which formed the present crust of our planet, of which this volume discloses a small but exciting detail. The materials of the Earth's crust are the rocks. In this book, the author expounds on how they were formed, why they altered, why they became the cradles of precious gemstones, how they are categorized, and how they are now exploited by man. What initiates the growth of gemstones? How do they crystallize? Why do gemstones of the same species, originating from different sources, vary? What causes the occurrence of varieties? Why do diamonds, unlike other precious stones, occur not near the Earth's surface in its crust, but deep down beneath it in the upper mantle? These are only a few of the entrancing subjects discussed in this enlightening volume. The reader learns that the Earth is surprisingly alive and altering constantly-sometimes through slow and equable changes and at times by violent and tremendous cataclysms, events from which gemstones issue.

Gemstones is the first attempt in English to bring together the geological, mineralogical and gemmological developments that have taken place during the last thirty years. Though there have been many gemstone books published in that time, most have been concerned, understandably and rightly, with the science of gem testing and have covered that area very well. Details of the geological occurrence of many of the classic gemstones, and of nearly all those which have only recently been discovered, have been less adequately dealt with. Coverage has been restricted to a number of papers in a wide variety of geological and mineralogical journals. Gemstones hopes to get the balance right. In the preparation of the book all the journals and monographs in the field have been consulted so that the book should stand for some years as the authority to which gemmologists and others turn in the first instance. Ease of reference and depth of coverage make Gemstones both a reference book and a bench book. Acknow ledgements I am grateful to Brian Jackson of the Department of Geology, Royal Museums of Scotland who read the manuscript and painstakingly indicated places where amendment or alteration was needed. I am also grateful to the publishers of the books on which the line illustrations are based. The colour plates present in the book derive from a number of sources, which I would like to acknowledge as follows. Plates 1, 4-15 and 17 Crown copyright reserved.