Tin is used chiefly in the making of tin plate, bronze, pewter, gun metal, and bell metal. Aluminum. The mineral called bauxite (a hydrous oxide of aluminum) is the great ore from which aluminum is obtained by an electrical process. Bauxite is noncrystalline, relatively light in weight, white to yellowish in color, and in the form of rounded grains, or earthy or claylike masses. The United States and France are the only two great producers of bauxite, most of which is treated for metallic aluminum. In 1918 the United States produced more than 100,000 tons of aluminum. In the United States the principal deposits are in Georgia, Alabama, and Arkansas. Bauxite is probably always a secondary mineral formed by decomposition of igneous rocks rich in certain aluminum silicate minerals. In some cases, as in the Georgia-Alabama region, the bauxite appears to have been formed and concentrated in deposits by hot solutions from uncooled igneous rocks. Aluminum is most used in the manufacture of wire for electric current transmission. It is also mixed with certain other metals like copper, zinc, magnesium, and tungsten to form special types of alloys, some of which possess remarkable tensile strength up to nearly 50,000 pounds per square inch. Aluminum is used in powdered form to generate very high temperatures in certain welding processes. It is also made into many kinds of utensils and instruments. Mercury. This metal, commonly known as "quicksilver," is of special interest because it is the only one which exists in liquid form at ordinary temperatures. The metal occurs in only small quantities in nature, most of it by far being obtained from the red mineral cinnabar described in the chapter on "Mineralogy." In order of importance the greatest quicksilver producing countries in 1916 were Italy, United States, Austria, and Spain. In the United States, California is by far the leading State, while Texas and Nevada are the only other important producers. In California most of the ore occurs in veins and irregular deposits in metamorphosed strata of Mesozoic and Cenozoic ages usually closely associated with igneous rocks. There, as well as in other parts of the world, hot vapors from igneous rocks carried the volatile ore upward and deposited it in fissures. Among the many uses of mercury are in making fulminate for explosives; making certain drugs and chemicals, pigments, electrical and physical apparatus; silvering mirrors; and in the amalgamation process of extracting gold and silver. OTHER ECONOMIC PRODUCTS Building Stones. Some of the principal features which should be considered in building stones are power to resist weathering, power to withstand heat, color, hardness, and density, and crushing strength. Building stones representing rocks of nearly all important geologic ages are widely distributed throughout the world.