This new edition has been considerably updated and expanded since the 5th edition (1994). Michael O’Donoghue is both the editor and principal contributor, having been responsible for 17 of the 31 chapters. In part I, there are two useful introductory chapters, the first, by Roger Harding being on the geological sources of gems, introducing the three main categories of rocks and the processes that formed them, before touching on the ages of gems, gem regions and gem recovery methods. This chapter ends with a useful note on the word ‘origin’ in certificates of authenticity: ‘geological source’ or ‘geographical locality’...

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