Garnet is the name of a group of minerals closely related in form and properties, but pre senting a number of varieties. They are all very complex aluminum silicates, in which various metallic oxides enter as components. The principal gem varieties are almandine, or precious garnet, the carbuncle of the ancients, containing considerable oxide of iron; its color is a deep, rather purplish or brownish red; pyrope, or Bohemian garnet, containing much magnesia, of a fine dark crimson, almost a ruby color. These two are the red garnets of jewelry; when cut en cabochon, that is, not facetted, but dome-shaped, they are called car buncles. Manganese garnet, or spessartite, is sometimes of a very beautiful orange-brown color; elegant gems of this kind have been found at Amelia Court House, Va. Uvoro vite, or chrome garnet, is a rare variety, of a brilliant dark green color, but the crystals are very small. Another green garnet of some what different composition, and with very bril liant lustre, from the Ural Mountains, is called demantoid, or Uralian emerald. Much fine garnet is found in the United States. North Carolina yields a beautiful variety that has been called rhodolite,— a brilliant light red gar net, between almandite and pyrope in composi tion; these are largely mined in the Cowee Val ley, in Macon County. New Mexico and Arizona produce fine pyropes. often misnamed "Arizona rubies," and equalling those of any other known locality. They are found where ants and centipedes have carried them out in making the galleries of their hills. In South Africa similar pyrope garnets found with the diamonds are termed "Cape rubies." Quartz is pure silica, the crystalline, rock crystal type occurring as six-sided crystals. It embraces a great number of the commoner gem stones, specific gravity about 2.6. These fall into three distinct groups,— The transparent colorless variety, rock crystal, then the purple amethyst which is colored by manganese, and finally the smoky topaz or smoky crystal, the ordinary black variety, and the intensely black amorion." When the black variety can be de colorized by heat, it changes first to a deep brown and then to a transparent yellow, some times becoming almost colorless. The original smoky quartz, deep brown in color, is called "cairngorm" ' • it is mostly used in Scotland and is the Scotch national stone. The lighter colors produced by decolorization by heat are known as Spanish topaz and citrine. Nearly all the so-called topaz of commerce is a quartz variety, not true topaz.
The cryptocrystalline variety, agate, is usu ally banded, and is generally the result of deposition of silica in the amygdules of a vol canic rock. The structure is in thin layers, even though they may not be visible to the eye. The principal varieties are chalcedony, gray and blue-gray, the apparently unbanded variety; when banded it is called ((banded agate." When this banded material has been broken and re cemented, it bears the name of "ruin agate"; if the bands are irregular in outline it is denominated "fortification agate." Chalcedony, when treated with iron salts and then highly heated, becomes red and is known as "car nelian"; if there be one or more layers, one of which is compact and impervious, it forms the "onyx" (from Greek word signifying "nail").
Should any one of two layers be pink, reddish or brown, it is termed ((sardonyx." The latter name has been applied to an artificially colored variety, from pale brown and pale red to brown; when black with a thin white, copper colored layer, it appears gray, and is called "nicolo." The name onyx is also applied to chalcedony saturated with boiling honey or blood, and then treated with sulphuric acid, the blood or honey becoming carbonized and making the entire stone a deep black. When chalcedony is stained a translucent red or i brown it is also called sardonyx, although it is really not an onyx, as it has only one layer.
The uncrystalline, or slightly crystalline, varieties are notably red jasper and green jasper. Whenjasper is green with red spots, due to the oxidation of the iron in the stone, it is called "bloodstone." When the stone is yellow, brown or black, the term jasper is also used.
Opal is silica containing from 5 per cent to 10 per cent of water. When it contains more than 5 per cent of water, the opal is liable to fracture; with 5 per cent or less, it is a stone of considerable durability. Magnificent speci mens of the white variety have been found in the mines of Hungary and in New South Wales, the white opals in New South Wales occurring in sandstone in which they occasionally re place wood, shells and the bones of reptiles. The black variety offers a velvet black field broken with the most intense red, green, yel low, blue and other colors. This is greatly prized and highly valued; it is found in the Lightning Ridge region in New South Wales. Many thousand fine gems have been brought from this locality, single stones selling for $5,000. The fire opals are a rich, red, honey or honey-red variety, containing a high per centage of water. The fire opal, or flame opal, found in Queretaro and other parts of Mexico is a rich honey-red —a brilliant variety with prominently large flames of light color, possibly due to inclusion of rutile (oxide of titanium). A colorless variety is also found, in which the play of color is in small flecks. This is known as the harlequin opal. Interesting opals re placing wood have been found in Humboldt County, Nev., brown, black and colorless.
Pendot, Chrysolite, or Olivine, deriving its name from its olive-green color, is a silicate of magnesia, found in magnificent examples in Egypt. Many magnificent specimens brought from the East are found in the church treas uries, dating from the time of the Crusades, notably at Cologne. They were then called emeralds. After a close study of the peridots here and in other ecclesiastical jewels, the opinion is expressed that almost if not quite all the fine examples in modern jewelry had been derived from this source. In 1900, gem chrysolites were found on the small volcanic island Seberget (also called Zebirget or Saint John) near the Egyptian coast of the Red Sea, an interesting discovery as it serves to con firm the ancient tale in early Greek and Latin authors that their chrysolite (which they called topaz) came from a mysterious °Serpent Isle in the Red Sea. They are also found in the Navajo Reservation in New Mexico, in small gems of considerable beauty; in Hawaii, as honey yellow and small gems; and at Lac La Hache, British Columbia.