galena, a gray lead sulfide (PbS), the chief ore mineral of lead. One of the most widely distributed sulfide minerals, it occurs in many different types of deposits, often in metalliferous veins, as at Broken Hill, Australia; Coeur d’Alene, Idaho, U.S.; Clausthal Zellerfeld, Ger.; and Cornwall, Eng. Large deposits also occur as replacements of limestone or dolomite (e.g., at Santa Eulalia, Mex.). Some deposits (e.g., at Darwin, Calif.) are of contact-metamorphic origin. Galena is found in cavities and brecciated (fractured) zones in limestone and chert, as in the extensive Mississippi River valley deposits, where 90 percent of the U.S. production of lead is mined. The mineral has occasionally been observed as a replacement of organic matter and sometimes occurs in coal beds.
Galena forms isometric crystals in which the ionic lattice is like that of sodium chloride. The mineral is easily weathered to secondary lead minerals, the upper part of galena deposits often containing cerussite, anglesite, and pyromorphite. Nodules of anglesite and cerussite with a banded structure and a galena core are common.
In many cases, galena contains silver and so is often mined as a source of silver as well as lead. Other commercially important minerals that frequently occur in close association with galena include antimony, copper, and zinc.