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THE CHEMISTRY,
PROPERTIES AND TESTS OF
PRECIOUS STONES
* * * * *
BY THE SAME AUTHOR
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* * * * *
THE CHEMISTRY, PROPERTIES
AND TESTS
OF
PRECIOUS STONES.
BY
JOHN MASTIN, M.A. D.SC. PH.D. LITT.D.
F.S A.SCOT. F.L.S. F.C.S. F.R.A.S. F.R.M.S. R.B.A.
_Author of "Parasites of Insects," "The True Analysis of Milk,"
"Plate-Culture and Staining of Amoebae," etc., etc._
_London_
E. & F. N. SPON, LIMITED, 57 HAYMARKET
_NEW YORK_
SPON & CHAMBERLAIN, 123 LIBERTY STREET
1911
Transcriber's note:
For Text: A word surrounded by a cedilla such as ~this~ signifies that
the word is bolded in the text. A word surrounded by underscores like
_this_ signifies the word is italics in the text. The italic and bold
markup for single italized letters or "foreign" abbreviations are
deleted for easier reading.
For numbers and equations: Parentheses have been added to clarify
fractions. Underscores before bracketed numbers in equations denote a
subscript.
CONTENTS
CHAPTER PAGE
I INTRODUCTORY 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
entirely different class to the minerals of a metallic nature. These
particular and non-metallic minerals, therefore, because of their
comparative rarity, rise pre-eminently above other minerals, and become
actually "precious."
This is, at the same time, but a comparative term, for it will readily
be understood that in the case of a sudden flooding of the market with
one class of stone, even if it should be one hitherto rare and
precious, there would be an equally sudden drop in the intrinsic value
of the jewel to such an extent as perhaps to wipe it out of the category
of precious stones. For instance, rubies were discovered long before
diamonds; then when diamonds were found these were considered much more
valuable till their abundance made them common, and they became of
little account. Rubies again asserted their position as chief of all
precious stones in value, and in many biblical references rubies are
quoted as being the symbol of the very acme of wealth, such as in
Proverbs, chapter iii., verses 13 and 15, where there are the passages,
"happy is the man that findeth wisdom ... she is more precious than
rubies"--and this, notwithstanding the enormous quantity of them at that
time obtained from the ruby mines of Ophir and Nubia, which were then
the chief sources of wealth.
It will also be remembered that Josephus relates how, at the fall of
Jerusalem, the spoil of gold was so great that Syria was inundated with
it, and the value of gold there quickly dropped to one-half; other
historians, also, speaking of this time, record such a glut of gold,
silver, and jewels in Syria, as made them of little value, which state
continued for some considerable period, till the untold wealth became
ruthlessly and wastefully scattered, when the normal values slowly
reasserted themselves.
Amongst so many varieties of these precious minerals, it cannot be
otherwise than that there should be important differences in their
various characteristics, though for a stone to have the slightest claim
to be classed as "precious" it must conform to several at least of the
following requirements:--It must withstand the action of light without
deterioration of its beauty, lustre, or substance, and it must be of
sufficient hardness to retain its form, purity and lustre under the
actions of warmth, reasonable wear, and the dust which falls upon it
during use; it must not be subject to chemical change, decomposition,
disintegration, or other alteration of its substance under exposure to
atmospheric air; otherwise it is useless for all practical purposes of
adornment or ornamentation.
There are certain other characteristics of these curious minerals which
may be classified briefly, thus:--Some stones owe their beauty to a
wonderful play of colour or fire, due to the action of light, quite
apart from the colour of the stone itself, and of this series the opal
may be taken as a type. In others, this splendid play of colour is
altogether absent, the colour being associated with the stone itself, in
its substance, the charm lying entirely in the superb transparency, the
ruby being taken as an example of this class of stone. Others, again,
have not only colour, but transparency and lustre, as in the coloured
diamonds, whilst the commoner well-known diamonds are extremely rich in
transparency and lustre, the play of light alone showing a considerable
amount of brilliancy and beauty of colour, though the stone itself is
clear. Still others are opaque, or semi-opaque, or practically free from
play of light and from lustre, owing their value and beauty entirely to
their richness of colour.
In all cases the value of the stone cannot be appreciated fully till the
gem is separated from its matrix and polished, and in some cases, such
as in that of the diamond, cut in variously shaped facets, on and
amongst which the light rays have power to play; other stones, such as
the opal, turquoise and the like, are cut or ground in flat,
dome-shaped, or other form, and then merely polished. It frequently
happens that only a small portion of even a large stone is of supreme
value or purity, the cutter often retaining as his perquisite the
smaller pieces and waste. These, if too small for setting, are ground
into powder and used to cut and polish other stones.
Broadly speaking, the greatest claim which a stone can possess in order
to be classed as precious is its rarity. To this may be added public
opinion, which is led for better or worse by the fashion of the moment.
For if the comparatively common amethyst should chance to be made
extraordinarily conspicuous by some society leader, it would at once
step from its humbler position as semi-precious, and rise to the nobler
classification of a truly precious stone, by reason of the demand
created for it, which would, in all probability, absorb the available
stock to rarity; and this despite the more entrancing beauty of the now
rarer stones.
The study of this section of mineralogy is one of intense interest, and
by understanding the nature, environment, chemical composition and the
properties of the stones, possibility of fraud is altogether precluded,
and there is induced in the mind--even of those with whom the study of
precious stones has no part commercially--an intelligent interest in the
sight or association of what might otherwise excite no more than a mere
glance of admiration or curiosity. There is scarcely any form of matter,
be it liquid, solid, or gaseous, but has yielded or is now yielding up
its secrets with more or less freedom to the scientist. By his method of
synthesis (which is the scientific name for putting substances together
in order to form new compounds out of their union) or of analysis (the
decomposing of bodies so as to divide or separate them into substances
of less complexity), particularly the latter, he slowly and surely
breaks down the substances undergoing examination into their various
constituents, reducing these still further till no more reduction is
possible, and he arrives at their elements. From their behaviour during
the many and varied processes through which they have passed he finds
out, with unerring accuracy, the exact proportions of their composition,
and, in many cases, the cause of their origin.
It may be thought that, knowing all this, it is strange that man does
not himself manufacture these rare gems, such as the diamond, but so far
he has only succeeded in making a few of microscopic size, altogether
useless except as scientific curiosities. The manner in which these
minute gems and spurious stones are manufactured, and the methods by
which they may readily be distinguished from real, will be dealt with in
due course.
The natural stones represent the slow chemical action of water, decay,
and association with, or near, other chemical substances or elements,
combined with the action of millions of years of time, and the unceasing
enormous pressure during that time of thousands, perhaps millions, of
tons of earth, rock, and the like, subjected, for a certain portion at
least of that period, to extremes of heat or cold, all of which
determine the nature of the gem. So that only in the earth itself,
under strictly natural conditions, can these rare substances be found at
all in any workable size; therefore they must be sought after
assiduously, with more or less speculative risk.