Silver. Native silver is not a very rare mineral and it is mined in certain parts of the world, but most of the metal is obtained from certain silver-bearing minerals, especially sulphides and a chloride. Silver crystallizes rather rarely in the isometric system. More commonly it occurs as irregular masses, plates, and wirelike forms. Characterized by its color, metallic luster, softness (less than 3 in the scale), and exceptional weight (specific gravity, 10.5). Usually occurs in vein deposits, commonly associated with other metals or metal-bearing minerals, especially copper. Sphalerite. A sulphide of zinc commonly in crystalline form belonging in the isometric system, especially in tetrahedral combination forms (see Figure 75b). Color, usually brown, yellow or nearly black with resinous luster. Hardness, nearly 4; specific gravity, 4. Several good cleavages, yielding fragments whose faces meet at 90 and 120 degrees. Sphalerite is a fairly common and widespread mineral, occurring nearly always in veins in most kinds of rocks. It is very often associated with other ores, particularly the great ore of lead (galena). Sphalerite is by far the greatest ore of zinc. Sulphur. Native sulphur. Crystallization, orthorhombic, usually in combination pyramidal forms. (See Figure 75h.) Characterized by yellow color, resinous luster, softness (about 2 in the scale), low specific gravity (about 2), and very poor cleavages. It has most commonly resulted from alteration of certain sulphur-bearing minerals, especially gypsum, the decomposition of which has yielded vast deposits. Some also of volcanic origin. Great quantities are used in making sulphuric acid, matches, gunpowder, fireworks, and for vulcanizing and bleaching rubber goods. Talc. Often called _steatite_. Monoclinic crystals rare. One perfect cleavage, yielding very thin, flexible leaves. Very soft (hardness, 1). Feels greasy, and looks waxy to pearly. Color, white, gray, to light green. Specific gravity, 2.8. Composition, a hydrous silicate of magnesia, much like that of serpentine. Talc is always of secondary origin, generally derived by chemical alteration of various common minerals rich in silicate of magnesia. _Soapstone_ is a common variety resulting from alteration of whole rock masses. Soapstone has many practical uses as for washtubs, table tops, electrical switchboards, hearthstones, stove and furnace linings, blackboards, gas tips, etc. Talc proper is used as a lubricant, to weight paper, in soap, as dustless crayon, talcum powder, etc.