Lead is used in making pipes, gutters, bullets, etc., and in its oxide forms in the manufacture of paints and glass. Eighty-three parts of lead with 17 parts of antimony make type metal. Lead and tin alloy to make solder. Lead and tin with small amounts of copper, zinc and antimony make pewter. The United States produce about 20% of the world’s supply of this metal. Galena PbS Pl. 17 _lead glance_ Occurs in cubes or cleavable masses; hardness 2.5; specific gravity 7.5; color lead-gray; streak lead-gray; luster metallic; opaque. While there is quite a group of lead-gray minerals, galena is easily identified by its cleavage, which is perfect in three directions parallel to the cube faces. Even a moderate blow of the hammer will shatter a mass of galena into small cubic pieces. The crystals often have the corners cut by octahedral faces, and occasionally the edges are beveled by dodecahedral faces. It is not uncommon to find crystals of large size, several inches across. If galena has 1 to 2% of bismuth as an impurity, curiously enough, the cleavage changes to octahedral, but this is a rare occurrence. Galena may occur as a primary mineral in veins associated with igneous intrusions, or in irregular masses in metamorphic rocks; but it is more often found in irregular masses in limestones, where the limestone has been dissolved, and the cavities thus formed, filled with secondary deposits of galena. It also occurs at the contact between igneous rocks and the adjacent rock, whatever this may be. Sometimes it is found in residual clays. Among the most important lead deposits are the Cœur d’Alene district in Idaho, where galena with a high percentage of silver is mined; the Leadville, Colo., district where lead, silver and gold occur together in veins; the Joplin, Mo., district, where lead and zinc ores occur together in irregular masses in limestones; and the Wisconsin district of similar character. When found galena is usually associated with sphalerite, argentite chalcopyrite, pyrite and calcite. It will be found in every state. Cerrusite PbCO₃ Pl. 18 _White lead ore_ Occurs in fibrous or compact masses, or in orthorhombic crystals, usually on galena; hardness 3.5; specific gravity 6.5; colorless; streak white; luster adamantine; transparent on thin edges. While the crystals of this mineral simulate hexagonal, they are actually orthorhombic, the simple form being an octahedron with two of its edges beveled, making double six-sided pyramids (see Pl. 18 A.) Usually prism faces are present. Twinning is common, both the simple contact sort, as shown on Plate 18 B, and also the sort in which three crystals have grown through each other, so as to make a six-rayed crystal. The considerable weight, and the fact that it effervesces in acid serve to identify cerrusite. When pure it is colorless, but impurities cause it to appear white, gray or grayish-black, and sometimes it has a tinge of blue or green.