Propylite

A low to medium-temperature metasomatic rock, sometimes a granofels or schist, generally formed by the propylitic alteration of basic to intermediate volcanic rocks around hydrothermal ore deposits or by plate magmatic alteration. Low-temperature varieties are principally composed of albite, calcite and chlorite; high-temperature varieties contain more epidote. A hydrothermally altered rock, often andesite, resembling a greenstone and containing calcite, chlorite, epidote, quartz, and minor pyrite or iron oxides. Propylite is common in mining districts of the Western United States, generally in the outermost subzone of hydrothermal alteration. See also propylitization. Ref: AGI