  This stone exhibits many varieties of color and of composition. The color probably most often thought of in connection with it is dark red, but it would be a mistake to suppose this the only color which it may manifest. Green, red, rose and brown are other colors which garnet transparent enough to be used as gems exhibits, while among opaque garnets may be found black and many varieties of the shades above mentioned. These variations of color are more or less connected with differences of composition which it may be well first of all to consider. Garnet as a mineral is, like most minerals used as precious stones, a silicate. United with the silica the element most commonly occurring is aluminum. If calcium be united with these two the variety of garnet known as grossularite, or essonite, or cinnamon stone, is produced. If magnesium takes the place of calcium, then pyrope is formed. If iron, we have almandite, and if manganese, spessartite. Another variety of garnet, andradite, is composed of calcium and iron in combination with silica, and still another, uvarovite, of calcium, chromium and silica. Though they seem to differ so much in composition, all kinds of garnet crystallize in the same system and are closely allied in all their properties, so that it is always an easy matter to distinguish garnet of any variety from other minerals. Garnet crystals may be of the twelve-sided form, known as dodecahedrons, the faces of which have the shape of rhombs, or the twenty-four-sided form known as trapezohedrons, the faces of which have the shape of trapeziums. Quite as commonly occur crystals which are combinations of these two forms, and then exhibit thirty-six faces, as in the crystal from Alaska shown in the accompanying illustration. Sometimes the crystals attain considerable size, some perfect ones from Colorado weighing fifteen pounds, while crystals two feet in diameter are reported from North Carolina. A curious feature of garnet crystals is that of often inclosing other minerals. The garnets from New Mexico, for instance, when broken open are sometimes found to contain a small grain of quartz. In the crystals from East Woodstock, Maine, only the outside shell is garnet and the interior is calcite. Other crystals are made up of layers of garnet and some other mineral. Garnet has a strong tendency to crystallize, and hence is usually found as crystals. The grains of garnet found in the sands of river beds and on beaches, though not often showing crystal form, may be really fragments of crystals. Garnet is one of the most common constituents of such sands because of its hardness and power of resisting decay. These properties enable it to endure after the other ingredients of the rocks of which it formed a part have been worn away. It is quite heavy as compared with the quartz of which the sand is mostly composed, and hence continually accumulates on a beach, while the quartz is in part blown away. In such localities it will always be found near the water line, because the waves, on account of its weight, can carry it but a slight distance inland. Practically all garnet is three and one-half times as heavy as water, and some four times as heavy. Garnet, as a rule, is somewhat harder than quartz, its hardness being 7½ in the scale of which quartz is 7. Some varieties are, however, somewhat softer. The hardness of garnet and its uneven fracture are properties which give it an extensive use for rubbing and polishing wood. For this purpose it is spread upon glued paper in the manner of sandpaper and is used similarly, but it is superior to the latter. Most varieties of garnet fuse quite readily before the blowpipe, and the globules thus formed will be magnetic if the garnet contains much iron. The green garnet, uvarovite, is almost infusible, however. Garnet is not much affected by ordinary acids, although it may be somewhat decomposed by long heating. GARNET.
The name garnet is said by some authorities to come from the Latin word granatus, meaning like a grain, and to have arisen in allusion to the resemblance of its crystals in color and size to the seeds of the pomegranate. The German word for garnet, granat, is the same as the Latin word. Others think the word derived from the Latin name of the cochineal insect in allusion to a similarity in color. The use of garnet for gem purposes seems to date back to the earliest times. Among the ornaments adorning the oldest Egyptian mummies there are frequently found necklaces containing garnet. The Romans prized the stone highly, and it is a gem very largely used at the present day, its hardness and durability and richness and permanency of color giving it all the qualities desired in a precious stone. Two varieties of garnet, almandite and pyrope, may exhibit the dark blood-red color especially ascribed to garnet. Almandite or almandine garnet derives its name from Alabanda, a city of Asia Minor, in the ancient district of Caria, whence garnet was first brought to the Romans. The finest almandite for a long time came from near the city of Sirian, in the old province of Pegu, Lower Burmah. While this was the center of supply, it is not known just where the garnets were obtained. Such garnets are still known as “Sirian” garnets. Their color tends toward the violet of the ruby and gives them a high value. There are several localities in Northern India where almandite is mined on a large scale, and the stone is much used in Indian jewelry. Some of these localities are Condapilly, Sarwar and Cacoria. Almandite is also found in Brazil, in Australia, in several localities in the Alps, and in the United States. Stones from all these regions are found suitable for cutting, the only qualifications needed being sufficient size and transparency and good color. The almandite of Alaska shown in the accompanying plate occurs in great quantities near the mouth of the Stickeen river, but has not been extensively cut on account of its being too opaque. Almandite usually occurs in metamorphic rocks, such as gneisses or mica schists; also in granite. It is also found in many gem gravels. From the ruby it can be distinguished, as can all varieties of garnet, by its lower hardness and single refraction of light. In artificial light, too, it borrows a yellow tint, rendering it less pleasing, while the color of ruby grows more intense. Pyrope, the magnesian variety of garnet, does not differ much in color from almandite. Both are dark red, but while almandite tends toward a violet tone, pyrope shades toward yellow. Pyrope is lighter than almandite, the specific gravity being 3.7 to 3.8, while that of almandite is 4.1 to 4.3. It is also less easily fusible. It rarely occurs in crystals, and where found in place is always associated with the magnesium-bearing rocks, peridotite or serpentine. It is thus probably always of eruptive origin. Pyrope is a characteristic constituent of the diamond-bearing rock of South Africa, and is the stone known in trade as “Cape ruby.” These garnets afford many excellent gems. The home of the pyrope, however, is and has been for many centuries, Bohemia. Here it is found in many localities, but chiefly in the northwestern part, near Teplitz and Berlin. The garnets are found in a gravel or conglomerate of Cretaceous age, resulting from the decomposition of a serpentine. Sometimes, however, they are found in the matrix and often associated with a brown opal. They are found by digging and separated by washing. Though of good quality the scones are small, those as large as a hazel nut being found but rarely. Although the Bohemian garnets have been known for many centuries, the industry of mining and cutting them on a large scale is said not to have assumed any special proportions until the advent of foreigners to Karlsbad. In this way a knowledge of the stones went out to other countries, and a demand sprang up which has led to the establishment of a great industry and made Of quite similar origin is the name carbuncle, a term applied to nearly all fiery red stones in Roman times, but now used to designate garnets cut in the oval form known as cabochon. The word carbuncle comes from the Latin word carbo, coal, and refers to the internal fire-like color and reflection of garnets. The calcium-aluminum variety of garnet, grossularite, cinnamon stone or essonite, is less used in jewelry than those above mentioned. It is usually yellow to brown in color, but may be rose red or pink, as in the specimen from Mexico shown in the accompanying plate. The yellow grossularites resemble in color the gem known as hyacinth and are sometimes sold in place of the latter, but true hyacinth is much heavier and doubly refracting. About the only essonites or cinnamon stones available for gems come from Ceylon. These are of good size and color. Those from Italy, shown in the accompanying plate, are too small to cut into gems, but surrounded as they are by light green chlorite and pyroxene, they make very pretty mineral specimens. Grossularite is almost always found in crystalline limestone. Green garnets are of two kinds, the calcium-iron garnet, known as demantoid, and the calcium-chromium garnet known as uvarovite. The demantoid garnets come only from the Urals. They have a rich green color and make beautiful gems when good ones can be found. The name demantoid refers to the diamond-like luster which they possess. The stone is also known as “Uralian emerald.” Uvarovite, named for Count Uvarov of Russia, also makes valuable gems if found in pieces of sufficient size and luster. It is found in Russia, in Pennsylvania and in Canada. Garnet has long been the birthstone of the month of January. “By her who in this month is born No gems save garnets should be worn. They will insure her constancy, True friendship and fidelity.” Such are the virtues ascribed to the garnet. That the stone has been known and used from the earliest times I have already remarked. Under the name of carbuncle mention is made of it in the literature of all ages, its impressive feature being usually the brilliant, fiery light which it gives forth. According to the Talmud, the only light which Noah had in the ark was afforded by a carbuncle, and there are many Oriental tales regarding the size and brilliancy of carbuncles owned by the potentates of the East. Occasionally carbuncles were engraved, and some fine garnet intaglios are still known. The greater abundance of the stone in modern times has led to its being less highly prized than formerly, and to its being put to other uses than mere adornment, but it perhaps contributes more largely to the comfort and happiness of the world as it is now used than could ever have been the case when it was the property only of kings. Oliver Cummings Farrington. |
|
