Chrome brick, besides being used in steel-making furnaces, is used in lining furnaces for making copper, nickel, and other metals. In these furnaces it is used in the bottoms and around the tap holes. Magnesite brick, as well as bauxite brick, have been used to replace chromite brick for this purpose. Chromium chemicals used for tanning are mainly sodium or potassium bichromates. About half of the bichromates produced in the United States is commonly used for tanning, the remainder being used for paints, pigments, dry colors, and dyes in the paint, printing and engraving, and textile industries. Chrome yellow, chrome orange, and chrome black are used in calico printing and dyeing. Chromic oxide, or chrome green, is an indelible pigment employed in printing banknotes. Various other chrome colors are used for paints and pigments as well as in the ceramic arts. The minor uses of chrome chemicals are many. GEOLOGICAL DISTRIBUTION Chromite throughout the world is associated with basic igneous rocks, such as peridotite or pyroxenite, or with the alteration products of these rocks, such as serpentine, talc schist, and related rocks. Chromite deposits are generally in the form of lenses, pods, or irregular masses that may occur singly or may be associated in groups. Besides being found as large bodies, chromite occurs as a minor constituent of these rocks, being widely disseminated through them as small specks and particles. Chromite that forms workable deposits is believed to have been separated out of the molten mass of basic igneous rock by segregation and to have formed separate bodies within the rock mass during the cooling. Most chromite deposits are found along the borders of intrusive masses not far from the contact of older rocks into which they are intruded. This is probably due to the formation of peripheral fractures during the cooling of the igneous mass, chromite being forced up into these openings. The action of convection-currents in the molten magma may also have resulted in localizing chromite bodies near the borders of the mass. However, bodies of chromite are quite abundant in other parts of the igneous masses as well, often being found at long distances from bordering rocks. By weathering of chromite-bearing igneous rock, chromite bodies are freed and occur as loose masses in resultant residual clays. Such bodies in clay are of commercial importance in many places. The breaking down of chromite-bearing rocks results in setting free disseminated specks and particles of chromite, and these may be transported and later deposited along streams flowing out of chromite-bearing areas. In this manner accumulations of chromite sands are formed. Besides chromite, these sands usually contain considerable quantities of other heavy minerals such as magnetite, ilmenite, garnet, and rutile, and the chromite in them is generally not available commercially. GEOGRAPHICAL DISTRIBUTION AND COMMERCIAL CONTROL