Precious Stones/Preface

by Arthur Herbert Church

PREFACE.

Since 1882, when the "Handbook of Precious Stones" was published, the volume has been several times reprinted from stereotype plates. Occasionally a few alterations and corrections were made in the text, but no opportunity occurred to improve the arrangement of the work or to add fresh material. The present issue, however, represents a thoroughly revised edition. A large number of paragraphs have been wholly rewritten, while so many additions have been made to the accounts given of the different kinds of precious stones and other beautiful minerals that the 112 pages of the original handbook have been increased to 140. Among the minerals which have now received fuller treatment may be named diamond, sapphire and ruby, and the different varieties of garnet and of zircon. But readers who desire to make themselves more intimately acquainted with the optical properties, the crystal-forms and intimate structure, the modes of occurrence and formation and the chemical composition and constitution of precious stones, will find it necessary to turn to works in which full details of these subjects are given. In this connection may be named the treatises of Dana, of Professor Lewis of Cambridge, Professor Maskelyne and Professor Miers, for in the pages of the present handbook only such scientific considerations find place as can be easily grasped, and which, at the same time, help to explain the beauty of precious stones and afford methods of identifying the different kinds.

The chief localities where precious stones are found have been named in Chapter VII. under the headings of the several species and varieties. But this subject cannot be adequately discussed without having recourse to maps, both geographical and geological, to which no space could be allotted in an elementary handbook. But there is one rich district which seems to require special notice here in order to remove what seems to be a prevalent misconception. In the body of the present handbook frequent references are made to the occurrence of many gem-stones in Ceylon. The search for these beautiful minerals and the traffic in them has, in fact, been going on in that island for ages, while the plumbago and mica industries are affairs of to-day. Yet it is strange that the importance of the Ceylon trade in precious stones remains unrecognised not only in newspaper correspondence but in official documents and in standard looks. One meets with such a statement as this—"Plumbago is, practically, our only mineral export"; and this, "The yield of gems in this island is not large, the total value of the annual production being said to be no more than ₤10,000." A glance at the true figures suffices to demonstrate the incorrectness of such statements. The value of plumbago exported from Ceylon in 1903 amounted to ₤119,316. Now the value of the gems exported in an average recent year by a single Colombo merchant was ₤30,000, while there are a score of other Ceylon gem merchants who together export no less than ₤200,000 worth annually. With casual sales to visitors to the island and to travelling dealers, a moderate estimate of the annual export of gems from Ceylon will be ₤300,000. The variety of kinds found is large, sapphires, spinels, alexandrites, chrysoberyls, beryls, topazes, catseyes, tourmalines, zircons, garnets and moonstones being the chief: diamonds, emeralds and turquoises do not occur, while pearls belong to a different category, being organic products. But it must be allowed that the precious stone industry constitutes now, as it has done for many centuries, an important feature in the resources of the island.

In concluding these prefatory notes I have much pleasure in acknowledging the help of Dr. C. A . MacMunn, to whose skill in spectroscopy many scientists are largely indebted. He drew for me the absorption-spectra of almandine and of zircon, reproduced in the coloured frontispiece. Although more exact in details, these drawings do not, I am glad to say, present any obvious differences from the corresponding figures in the plate issued in 1882 with the first edition of this handbook. But they do show a marked superiority over the spectra figured in subsequent issues. The nine upper figures in the Frontispiece show the twin colours of certain precious stones, figs. 1 to 6 representing the hues as seen in the dichroiscope.

A.H.C.

Kew Gardens, February, 1905.