  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. QUARTZ (crystalline.)
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, 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. |
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