This is the most abundant, most durable and most indestructible of
common minerals. There is scarcely a sand beach, field or mountain side
upon which this mineral cannot be found in some form or other. Its
abundance is due not so much to its excess in quantity in the underlying
rocks as to the fact that, being harder and less easily decomposed than
other minerals, it remains after they are worn away.
Though so common, it appears in so great a variety of colors and
different kinds of structure that a large collection of minerals
_looking_ very much unlike might all be made up of Quartz. If they were
all of Quartz they would have the following characteristics: Hardness, 7
(cannot be scratched with a knife blade); specific gravity, two and a
half times as heavy as water; no cleavage; fracture conchoidal
(shell-like); infusible before the blowpipe; insoluble in common acids.
The numerous varieties of Quartz can be grouped into two classes, the
pheno-crystalline (plainly crystalline) and the crypto-crystalline
(obscurely crystalline). This article deals with the plainly crystalline
varieties. These include, among other varieties, rock crystal, amethyst,
rose quartz, smoky quartz, and sagenitic quartz. These varieties all
occur in well formed crystals, and all have a vitreous luster, i. e.,
luster like that of glass. The differences between them are almost
exclusively differences of color.
Rock Crystal—This is quartz in its purest form. Typical rock crystal is
perfectly transparent and colorless, but the mineral is often more or
less clouded and opaque. By the ancients it was supposed to be petrified
ice, and hence the Greeks applied to it their word for ice, from which
we get our word crystal. The belief in its ice origin survived to a
comparatively late period, for in 1676 Robert Boyle opposed the idea,
stating that the quartz could not be ice, first because it was two and a
half times as heavy as water, and second because it was found in
tropical countries. The belief of the ancients probably came largely
from the fact that the quartz they knew was obtained from the peaks of
the Alps. They reasoned that it was ice that was frozen so hard that it
would never melt. Fortunately our present knowledge of chemistry
prevents us from any longer confounding the two substances, for we know
Quartz is oxide of silicon while water is oxide of hydrogen.
Quartz in the form of rock crystal occurs in all parts of the globe, and
for the most part in well-formed crystals. These crystals are usually
six-sided, and usually have the form of a prism capped by a pyramid. Hot
Springs, Arkansas, and Little Falls, New York, are the best known
localities in our own country for this form of crystallized quartz. The
Little Falls crystals are exceptionally brilliant and well formed. From
this locality and others the material, cut or uncut, is often known as
diamonds, and sold as such. Such stones can, of course, be easily
distinguished from true diamond, for while they will scratch glass,
their hardness is much below that of the king of gems and they utterly
lack the internal fire of the latter.
Rock crystal occurring in large, clear masses is often cut into
ornamental and useful objects such as seals and paperweights, and
especially into balls. The latter industry flourishes especially in
Japan, and perfectly clear quartz balls six inches in diameter are made
there.
Rock crystal is also used extensively to cut into eyeglasses and
spectacles in place of glass, some considering it less detrimental to
the eyes than glass. It is also occasionally used for mirrors, it being
superior to glass for this purpose, in that it does not detract from the
rosiness of the complexion.
Among the ancients rock crystal was much more highly prized than among
us, as it answered them many of the purposes for which we now find glass
more suitable and cheaper. Wine glasses were made from it, though of
course at great cost, a thousand dollars being considered a small price
for one. Lenses of rock crystal were used to concentrate the rays of the
sun for cauterizing wounds and also to light fires, especially
sacrificial ones. Roman ladies were also accustomed to carry balls of
rock crystal in their hands in summer for the sake of the coolness they
afforded. The ladies of Japan are said to do the same at the present
day.
[Illustration: QUARTZ (crystalline.)]
Top row:
Rutilated Quartz, polished (Brazil.)
Amethyst (Virginia.)
Center:
Smoky Quartz (Switzerland.)
Bottom row:
Rose Quartz (Black Hills.)
Amethyst (Montana.)
The stone was in former times often stained different colors, and thus
all sorts of imitation gems were produced. The modern method of making
doublets has now superseded this art.
Amethyst.—This is the name given to the violet or purple varieties of
crystallized quartz. The color has often been supposed to be due to
small quantities of oxide of manganese, but is more probably the result
of a content of organic matter, as the color can usually be mostly
burned out by heating the stone. By partial heating the color is changed
to yellow, and much so-called citrine is simply burned amethyst.
Quartz having in a general way the amethystine color is comparatively
common, but for gem purposes only that transparent and of good color is
available.
Important localities for gem amethysts are Southern Brazil, the Ural
Mountains, Ceylon, and occasional finds in the States of Maine, North
Carolina, Pennsylvania and Montana in our own country.
Very commonly where crystallized quartz occurs, crystals of an
amethystine hue are to be found, so that to enumerate localities of the
mineral would be a considerable task. Good cut amethysts command a fair
price, though they are much less valuable than formerly. Three or four
dollars a carat is a fair price at the present time. At the beginning of
this century Queen Charlotte of England is known to have paid $10,000
for an amethyst for which $500 could now hardly be realized. One reason
for the greater esteem in which amethyst was formerly held is probably
the virtue ascribed to it of shielding its wearer from the effects of
drinking too much wine. Its name is derived from two Greek words,
meaning “not to inebriate.” The drinking cups of the Romans were often
made of it, partly for the above reason and partly on account of their
belief that any poison placed in such a cup would be rendered harmless.
Amethyst is the “birth stone” of the month of February, and St.
Valentine is said always to have worn an amethyst.
“The February born shall find
Sincerity and peace of mind,
Freedom from passion and from care
If they an amethyst will wear.”
Rose Quartz.—This form of quartz, the color of which is indicated by its
name, is rarely of sufficient transparency to be prized as a gem. Cut,
however, into various ornaments, it makes objects of considerable
beauty. Its luster, instead of being glassy like that of other forms of
quartz, is nearly always more or less greasy. The ingredient which gives
its color is not known. It is probably some organic matter, since the
color disappears on heating and, unfortunately for the extended use of
the stone, fades considerably on exposure to light. There are numerous
localities whence rose quartz of good color may be obtained, although it
is not of so common occurrence as most other varieties of quartz. The
best rose quartz in this country comes from Oxford County, Maine, and
the Black Hills. Foreign localities are the Urals, Brazil and Ceylon.
Smoky Quartz.—This variety of quartz is often known as “smoky topaz,” a
misleading term, since the mineral is not topaz at all. As its name
implies, its color is like that of smoked glass, all gradations
occurring between a mere tinge to color so dark as to render the mineral
practically opaque. The color often varies considerably in the same
crystal, being darker and lighter in spots. The coloring matter is
undoubtedly carbonaceous and organic in nature, for when a crystal is
heated it gives off a smell of burning organic matter, and by heating
for some length of time the coloring may be entirely burned out. At an
intermediate stage in such heating the color becomes brown or yellow,
and stones of this color are often cut as gems and known by the name of
“Spanish topaz” or “citrine.” True citrine is, however, transparent
quartz with a natural yellow color. The most remarkable crystals of
smoky quartz known are some that were found in 1868 in a hollow in
granite in a locality in the Canton Uri, Switzerland. About 3,000 pounds
of well formed crystals were there found, the largest and best of which
are preserved in the Berne Museum. They are so unique that special names
have been given them. One about two and one-half feet long, and weighing
nearly four hundred pounds, is known as the “Grandfather”; another,
somewhat smaller, but more perfect in form, as the “King,” and two of
nearly equal size, weighing about one hundred and forty pounds each, are
called “Castor and Pollux.” The smaller crystals obtained from this and
neighboring regions in the Alps are for the most part of great
perfection of form and color. Aside from these localities in the Alps,
the most remarkable crystals of smoky quartz come from the region of
Pike’s Peak, in our own country. While not reaching the size of the
Alpine crystals, they are often perfect in form and color, and gems to
the value of thousands of dollars are annually cut from the supply there
obtained. Alexander County, North Carolina, also furnishes many
crystals. Smoky quartz may be called the national stone of Scotland, the
name by which it is known being “Cairngorm stone,” from the locality
where the best crystals are obtained.
Sagenitic Quartz.—This form of quartz, also known as “sagenite,” “fleche
d’amour” (love’s arrow), “Venus’ hair stone,” and, if the included
mineral be rutile, “rutilated quartz,” is rock crystal containing
inclusions of other minerals in hair-like or thread-like forms. Of the
minerals so included, rutile is the most common, but tourmaline,
hornblende, epidote and others occur. These minerals are formed in the
quartz doubtless by crystallizing simultaneously with that mineral, or
“host,” as it is called. The arrangement often gives a stone of great
beauty, especially when the rutile is more or less transparent and has a
blood red color. The Japanese frequently polish the surfaces of such
crystals of quartz to make the interior structure better visible.
Specimens are also obtained from Madagascar, Brazil, and North Carolina
in our own country. When the fibers of the included mineral are smaller
and more abundant, the forms of quartz known as “cat’s eye” and “tiger
eye” are produced. The reflection of light from the surfaces of the
fibers gives the glittering effect known as chatoyancy. Nearly all the
“tiger eye” in use at the present time comes from South Africa; the
cat’s eye from Bohemia and Ceylon.
Oliver Cummings Farrington.