Supergene Minerals

minerals that form in a supergene zone—that is, in the uppermost part of the earth’s crust—at low temperatures and pressures. They are characterized by hydration (the entry of molecular water or hydroxyl into the crystal lattice) and a high degree of oxidation of the elements (iron, manganese, sulfur, and others). The weathering of silicate rocks yields clay minerals, which are among the most widespread supergene minerals.

The supergene minerals include many compounds of several types: oxides, hydroxides, salts of oxy acids (carbonates, sulfates, nitrates, phosphates, and so on), and chlorides. Supergene minerals in oxidation zones of ore deposits —compounds of iron, copper, lead, and zinc (malachite, cerussite, anglesite, and so on)—are of great practical significance. The composition of supergene minerals from the same initial rock or ore depends on the climatic conditions under which the supergene processes take place. For example, the weathering of silicate rocks under mild climatic conditions leads to the formation of clay minerals, primarily of the hydromica type; weathering of the same rocks in the tropics yields kaolin clays and aluminum-oxide hydrates (bauxites).