Both the copper carbonates, azurite or chessylite, and malachite, make effective polished stones. The latter is also worked into various ornamental objects; it occurs in fibrous masses, the grained character of which look well in the polished section. Its colour is a bright green, to which it owes its name, from μαλακή, mallows. Its composition is represented by the formula CuCO_{3}.Cu(OH)_{2}, and it is the more stable form, since azurite is frequently found altered to it. It has biaxial double refraction, and the indices are about 1·88; the specific gravity is 4·01, and hardness about 3½ to 4 on Mohs’s scale. It is found in large masses at the copper mines of Nizhni Tagilsk in the Ural Mountains, where it is mined as an ornamental stone; it also accompanies the copper ores in many parts of the world, for instance Cuba, Chili, and Australia. Azurite, so called on account of its beautiful blue colour, is rarer, but, unlike malachite, is generally in the form of crystals. Beautiful specimens have come from Chessy, near Lyons, France, and Bisbee, Arizona, U.S.A. The composition corresponds to the formula 2CuCO_{3}, Cu(OH)_{2}. The specific gravity is 3·80, and hardness about 3½ to 4. Chrysocolla occurs in blue and bluish-green earthy masses, with an enamel-like texture, which in some instances can be worked and polished. Being the result of the decomposition of copper ores, it varies considerably in hardness, ranging from 2 to 4 on Mohs’s scale. Its composition approaches to the formula CuSiO_{3}.2H_{2}O, but it invariably contains impurities. It is very light, the density being only about 2·2. Steatite, or soapstone, is a massive foliated silicate of magnesium corresponding to the formula H_{2}Mg_{3}Si_{4}O_{12}, which is one of the softest of mineral substances, representing the degree 1 on Mohs’s scale, but in massive pieces is harder owing to the intermixture of other substances with it. It has a peculiar greasy feeling to the touch, due to its softness. The specific gravity is about 2·75. The Chinese carve images out of the yellowish and brownish pieces. Meerschaum, a silicate of magnesium corresponding to the formula H_{4}Mg_{2}Si_{3}O_{10}, is familiar to every smoker as a material for pipe-bowls. It is very light, the specific gravity being only 2·0, and soft, the hardness being about 2 to 2½ on Mohs’s scale. When found, it is pure white in colour, and answers to its name, a German word signifying sea-foam. It comes from Asia Minor.