These are four recently published books on gemstones and gemstone identification. The first two of these titles, Gems and Tables of Gemstone Identification, are books written for the specialist gemmologist and the other two are popular guides aim at a more general market. One striking feature of all, is the breadth of their definition of what constitutes a gemstone. This stretches well beyond the popular gems – diamond, ruby, emerald, sapphire, opal and pearl – into really quite obscure minerals.

The new edition of Gems was edited and largely written by Michael O'Donoghue, a well known gemmologist. This is the sixth edition of Robert Webster's book originally published in 1962 and it has been for many years the standard reference work on gemmology in English. The new edition replaces the fifth edition, published by Butterworth in 1994, and preparation of the new edition has involved extensively rewriting and reorganization. The gem testing section prominent in the previous editions has been omitted, enabling the current edition to be over 200 pages shorter than the fifth edition. The new edition is divided in two parts. Part 1 is a brief introduction to the geological sources of gems and the crystallization of gem materials (66 pages in total). This is a concise outline of the essentials of geology and crystallography for the gemmologist. Part 2 consists of a series of chapters on individual gem minerals or groups staring with diamond. The longest chapter, some 80 pages, is devoted to pearls. The less common gemstones are grouped together in Chapter 23 and there are also chapters on synthetic gemstones, composite gemstones, gemstone simulants and plastics. The primary literature of the gems is extensively referenced throughout and appears to be updated to the end of 2004. Gems is the reference book for the jeweller, professional and advanced amateur gemmologist.

Tables of Gemstone Identification is also a work aimed at the advanced gemmologist and contains a very comprehensive set of tables of the optical and essential physical properties of gem minerals. Table 1 list gems by refractive index, as measuring the RI using a refractometer remains the simplest method of identifying cut gems in jewellery. Table 2 lists opaque and translucent stones. Table 3 list gems by density while Table 4 give absorption spectra for the various gem minerals. Table 5 is an alphabetical index. In addition there is a series of specialist tables for various mineral groups such as the garnets. This book is really only of interest to the gemmologist as a bench manual for gemstone identification.

Arthur Thomas's Gemstones provides a popular guide to the gem kingdom and is lavishly illustrated with a wonderful series of colour images showing both cut and rough stones. A somewhat idiosyncratic feature of the book is that the gemstones are group by crystal system and then ordered by decreasing hardness. The book also provides a brief treatment of gem cutting and enhancement. Schumann's Gemstones of the World is a popular full-colour guide to gems and lists both precious and semiprecious stones. A feature of the guide is the lavish use of colour photography. Schumann adopts the more traditional arrangement of gems dividing them into two groups: the best-known gems with diamond, sapphire, ruby, etc. and followed by the lesser-known gems including andalusite, benitoite, and scapolite.

O'Donoghue's Gems should be in every Earth Science library, and is highly recommended. The new edition is such a significant update that libraries should buy it to replace the fifth edition. Schumann is a beautiful and inexpensive little guidebook and is also recommended.