Some Ornamental Stones

Agalmatolite: A compact, soft material consisting of impure mixtures of one or several minerals. Most agalmatolite is composed of steatite, or soapstone, which is a hydrated mag­nesium silicate. It may also be pyrophyllite, which is a hydrous aluminum silicate. What­ever the soft, soapy-feeling material may be, it is gray, green, brown, black, white, yellowish, or often mixtures of several of these colors. The material is easily carved with a knife.

Alabaster: A white, very soft, and very fine-grained variety of a mineral called gyp­ sum. Gypsum is hydrous calcium sulfate, is very common, and has a hardness of only 2. The softness of the mineral plus its uniform texture make it ideal for carving purposes. There is also a fine fibrous variety of gypsum known as satin spar because of its pearly sheen.

Amazons tone: The feldspar family of min­erals has several species. One of them, micro-cline, is a rather common potassium aluminum silicate. Occasionally, the species is found in a beautiful, opaque, bright green—presumably the color of the Amazon River. Because it is sufficiently hard and durable, and cuts and polishes well, it is used for costume jewelry.

Anthracite: A very hard variety of coal which can be cut and polished easily. It once was popular for carving curios and souvenirs of the coal industry and coal-producing towns. Some of it was cut and polished for jewelry. It resembles the best jet, but takes a more bril­liant polish and is harder than jet.

Aventurine: Most aventurine is a variety of quartz containing large numbers of inclu­sions of tiny scales of mica, hematite, or other platy material. These highly reflective plates give the material a flashing, spangled effect in bright light. Some feldspar produces the same effect with similar inclusions.

Californite: Although it resembles jade, this compact, somewhat translucent green mineral is actually an attractive variety of ido-crase. Idocrase is a complex calcium aluminum silicate, and the variety name, of course, comes from its best-known occurrence in California.

Chrysocolla: Most of the gem material called chrysocolla circulating among amateur cutters and in the gem trade is not truly this very soft, hydrous copper silicate mineral. Rather, it is quartz which is colored bright blue to greenish-blue by varying amounts of impurities consisting of chrysocolla or other copper mineral species. The quartz contributes its hardness and ability to take a good polish. The lovely color is still that of true chrysocolla.

Crocidolite: Again, the available "crocid-olite" is not actually this species, but is quartz which has either replaced or enclosed the orig­inal fibrous, asbestos-like crocidolite mass. Chemical changes in the original crocidolite color the mass in shades of yellow, brown, and blue. Because of its fibrous nature, crocidolite, when properly cut and polished, is the source of "tiger eye." Crocidolite figures, ash trays, bowls, bookends, and such, are quite attractive and popular.

Jet: As suggested earlier, jet is a black variety of lignite, or of brown coal. Like anthracite coal, it has a compact texture and polishes well, although it scratches and abrades so easily that constant repolishing is necessary.

Labradorite: This is a calcium sodium sil­icate, one of the series of closely related plagio-clase feldspars which vary in relative amounts of calcium and sodium present. Pure labrador­ite has been found in flawless, transparent, colorless to yellowish to red pieces large enough to cut good, faceted gems. The best-known labradorite variety is the kind which exhibits flashes of spectral interference colors (described in Chapter 2). The intense and gorgeous play of many colors is caused by its thin-layered structure, or by thin, plate-shaped inclusions of other minerals, such as magnetite.

Lapis lazuli: The material most often cut and polished as lapis lazuli—literally, "blue rock"—is really a rock. It is composed of a highly variable mixture of the minerals lazurite (primarily a blue sodium aluminum silicate), pyrite (in brassy colored spots) and calcite (as white streaks and blotches through the blue). The best lapis lazuli is uniformly deep blue in color and consists almost totally of lazurite.

Malachite: The name malachite-green, when referring to pigments, evokes an image of a deep leaf-green color. This hydrated cop­per carbonate mineral has such a beautiful color—often distributed in interesting agate­like patterns—that it has remained universally popular for ornamental purposes for hundreds of years. Its extensive use in beautiful inlay work, such as that in Imperial Russian palaces, is legendary. Soft and subject to chemical at­tack, it is nevertheless prized above many other ornamental stones. Some malachite is quite beautiful when associated with bright blue azurite, another hydrated copper carbonate.

Mexican Onyx: Sometimes this soft, orna­mental stone is known as cave onyx, or simply as onyx. It differs markedly from true onyx because it is not black and is much softer. It is a kind of banded, mottled, and clouded marble composed of calcite in various shades of green, brown, and off-white. Mexican crafts­men cut the soft material into a variety of objects for the curio and tourist trade.

Obsidian: This natural glass, resulting from rapid cooling of molten volcanic rock, occurs in colors ranging from green through brown to black. Common enough to be used for carving inexpensive figures and other curios, it is sometimes difficult to distinguish from man-made glasses.

Rhodochrosite: This is an unusual man­ganese mineral in that it has an intense, rosy-pink color instead of the usual black. It is an opaque, soft, easily carved and shaped manga­nese carbonate which is valued for general ornamental purposes. The best material comes from Argentina, some of it showing interesting agate-like banded patterns.

Rhodonite: Again, the prefix "rhodo" in this name means a pink mineral. It is a manga­nese silicate and, unlike rhodochrosite, is fairly hard at about 6. This makes it more difficult to fashion, but at the same time it is more du­rable. The fact that it is too opaque restricts its use to ornamental purposes, although it is cut and polished for inexpensive jewelry.

Serpentine: Because it may resemble jade so closely, serpentine is difficult to distinguish, even for experts. Generally, however, it is softer and has a lower specific gravity. There is a variety of serpentine called bowenite, with a hardness up to 6 and a specific gravity up to 2.9, which brings its characteristics very close to those of nephrite jade. Like jade, serpentine is variable in color and commonly found in black, brown, tan, white, and green masses. Capitalizing on its resemblance, serpentine is used to simulate jade carvings, although it is often beautiful enough to stand on its own merits. Verd antique is a white, calcite-veined variety often cut into large slabs for use as an ornamental decorative facing for buildings.

Variscite: With occurrences limited to a couple of small deposits in the United States, this hydrous aluminum phosphate has not been widely used as an ornamental stone. It cuts and polishes well, has a light but intense green color—often with interesting patterns of associated minerals—and is hard enough at 5 to be useful as cut stones for inexpensive jewelry.