1

II THE ORIGIN OF PRECIOUS STONES 7

III PHYSICAL PROPERTIES--(A) CRYSTALLINE STRUCTURE 13

IV " " (B) CLEAVAGE 19

V " " (C) LIGHT 26

VI " " (D) COLOUR 32

VII " " (E) HARDNESS 39

VIII " " (F) SPECIFIC GRAVITY 45

IX " " (G) HEAT 52

X " " (H) MAGNETIC AND ELECTRIC INFLUENCES 57

XI THE CUTTING OF PRECIOUS STONES 62

XII IMITATIONS, AND SOME OF THE TESTS OF PRECIOUS STONES 70

XIII VARIOUS PRECIOUS STONES 80

XIV " " " (_continued_) 88

XV " " " " 98

PREFACE

Some little time ago certain London diamond merchants and wholesale
dealers in precious stones made the suggestion to me to write a work on
this section of mineralogy, as there did not appear to be any giving
exactly the information most needed.

Finding there was a call for such a book I have written the present
volume in order to meet this want, and I trust that this handbook will
prove useful, not only to the expert and to those requiring certain
technical information, but also to the general public, whose interest in
this entrancing subject may be simply that of pleasure in the purchase,
possession, or collection of precious stones, or even in the mere
examination of them through the plate-glass of a jeweller's window.

JOHN MASTIN.

TOTLEY BROOK,
NEAR SHEFFIELD.

_June 1911._

THE CHEMISTRY, PROPERTIES AND TESTS OF PRECIOUS STONES

CHAPTER I.

INTRODUCTORY.

What constitutes a precious stone is the question which, at the onset,
rises in the mind, and this question, simple as it seems, is one by no
means easy to answer, since what may be considered precious at one time,
may cease to be so at another.

There are, however, certain minerals which possess distinctive features
in their qualities of hardness, colour, transparency, refractability or
double refractability to light-beams, which qualities place them in an
enti