[Illustration: _PLATE I_ _Frontispiece_ GEM-STONES] GEM-STONES AND THEIR DISTINCTIVE CHARACTERS BY G. F. HERBERT SMITH M.A., D.Sc. OF THE BRITISH MUSEUM (NATURAL HISTORY) WITH MANY DIAGRAMS AND THIRTY-TWO PLATES OF WHICH THREE ARE IN COLOUR THIRD EDITION METHUEN & CO. LTD. 36 ESSEX STREET W.C. LONDON _First Published_ _March 21st 1910_ _Second Edition_ _June_ _1913_ _Third Edition_ _1919_ PREFACE In this edition the opportunity has been taken to correct a few misprints and mistakes that have been discovered in the first, and to alter slightly one or two paragraphs, but otherwise no change has been made. G. F. H. S. WANDSWORTH COMMON, S.W. PREFACE TO THE FIRST EDITION It has been my endeavour to provide in this book a concise, yet sufficiently complete, account of the physical characters of the mineral species which find service in jewellery, and of the methods available for determining their principal physical constants to enable a reader, even if previously unacquainted with the subject, to have at hand all the information requisite for the sure identification of any cut stone which may be met with. For several reasons I have dealt somewhat more fully with the branches of science closely connected with the properties of crystallized matter than has been customary hitherto in even the most comprehensive books on precious stones. Recent years have witnessed many changes in the jewellery world. Gem-stones are no longer entirely drawn from a few well-marked mineral species, which are, on the whole, easily distinguishable from one another, and it becomes increasingly difficult for even the most experienced eye to recognize a cut stone with unerring certainty. So long as the only confusion lay between precious stones and paste imitations an ordinary file was the solitary piece of apparatus required by the jeweller, but now recourse must be had to more discriminative tests, such as the refractive index or the specific gravity, the determination of which calls for a little knowledge and skill. Concurrently, a keener interest is being taken in the scientific aspect of gem-stones by the public at large, who are attracted to them mainly by æsthetic considerations.