Since it was published in 1962, Gems has become universally recognized as the most comprehensive and authoritative treatise on gem materials in the English language. Now in its sixth edition, it has been revised for relevance to today's practice.It includes an expanded encyclopaedic section, and offers a descriptive account of all gem materials used as ornament, along with their synthetic counterparts and the materials used over the centuries to imitate them.Editor Michael O'Donoghue has been assisted by a team of specialists to make this sixth edition of Gems an invaluable gemmological reference work which caters for professional jewellers, student gemmologists, and collectors of gems alike.