Hematite is used as a polishing agent, as a pigment in paint, and, of course, as an ore of metallic iron. In the smelting of iron from hematite the ore is mixed in a huge, chimney-shaped blast furnace with coke (from coal) and limestone. Air is blown into the furnace as into a blacksmith’s forge; and the coke and gasses, burning at an incandescent heat, take the oxygen from the Fe₂O₃, leaving metallic iron which melts and is run out of the furnace at periodic intervals. Thus the smelting process is the opposite of the rusting process. The impurities and cinder run out as molten slag. Limonite [Illustration: Dark brown limonite.] [Illustration: Stalactitic limonite from southeastern Missouri.] Limonite is a heavy, yellow to brown, or brownish black mineral which always leaves a yellow to brown mark or streak when rubbed across a hard white rock or unglazed porcelain. It usually has a dull luster on a broken surface, and may vary from thumb-nail hardness to almost that of steel. The distinguishing test is its yellow to brown streak. In composition limonite is iron oxide which contains more or less water chemically combined, Fe₂O₃·nH₂O. That is, it may be dried bone-dry at the temperature of boiling water, but upon heating to redness the additional, chemically held water will be driven off. Limonite is ordinarily formed from the weathering of other iron-containing minerals (pyrite, for example) and is therefore a wide-spread mineral in surface rock, in films on pools of water, and in soil, all of which it colors yellow to brown. In fact, almost all of the yellow to brown inorganic mineral color and stain seen in nature is that of limonite. Commercial deposits of limonite occur in southeastern Missouri where large boulders, discontinuous and irregular lenses or beds, pipes, nodules, and gravel to clay-sized particles of the mineral are associated with the cherty, gravelly residual clay. Usually the ore is crushed, hand-sorted, and washed preparatory to concentration for shipment to a furnace or for use in cement manufacture. As in the case of hematite, unless one has a deposit amounting to thousands of tons of ore it has little commercial value, and unless the mineral is relatively pure it can not be used. Paint Ore or Red Ochre An intensely red-colored, clayey iron ore has been mined for paint pigment in several deposits in south central Missouri. It occurs in sink hole deposits like those containing fire clay. Brown ocher may be available from southeast Missouri. Iron Band Diaspore Shells of red or reddish brown iron oxide occur about cores of diaspore clay in some of those deposits south of the Missouri River. Previously this material had no value, but in the last few years it has been purchased for and shipped to a cement company, which used it in the manufacture of cement. Diaspore clay is discussed elsewhere in this pamphlet.