According to the editors, the latest (5th) edition of the American Geological Institute's Glossary of Geology contains some 39,300 entries running from ‘A’ (mass number) to ‘zykalite’ (a greyish-white orthorhombic mineral). Over 3600 of the entries are new and nearly 13,000 have been updated; 5300 of them are mineral names, an increase of around 1000, and they constitute the largest single group of terms, reflecting the slight bias of the work. I looked in vain for the terms theropod, cynodont and perissodactyl and yet some 10% of the definitions are apparently devoted to palaeontology.

The glossary project started off in 1957 with a 14,000 term glossary supplement published in collaboration with the National Academy of Sciences. That developed into the first one volume edition in 1972 with some 33,000 terms and has grown steadily ever since. However, it is worth pointing out that the process has not been one of continuing addition of terms but also a regular weeding out of several thousand obsolete terms. Usefully, references to academic papers of significance to the definition of some terms are also given.

As far as I am aware this is the only English language glossary of geology written and checked by a significant number of experts across the whole field of the subject. As Klaus Neuendorf says in his preface, ‘the authority of this Glossary rests on the expertise of more than a hundred eminent geoscientists who participated as volunteers in the arduous task of a two-level review’. He goes on to invite users to suggest additions and corrections for future versions of the Glossary and these can be submitted via email to glossary@agiweb.org. So it is up to any slightly disgruntled user who cannot find their pet terms, or think others ought to be emended, to do something about it. This is an essential volume for any earth science library.