skarn

skarn, in geology, metamorphic zone developed in the contact area around igneous rock intrusions when carbonate sedimentary rocks are invaded by large amounts of silicon, aluminum, iron, and magnesium. The minerals commonly present in a skarn include iron oxides, calc-silicates (wollastonite, diopside, forsterite), andradite and grossularite garnet, epidote, and calcite. Many skarns also include ore minerals; several productive deposits of copper or other base metals have been found in and adjacent to skarns. Granitic and dioritic magmas are most commonly associated with skarns. Skarns can be zoned, with the inner zones successively replacing the outer ones as the wave of metamorphism moves through the surrounding rocks.