skarn

Skarns or tactites are calcium-bearing calc–silicate rocks. Skarns are most often formed at the contact zone between intrusions of granitic magma bodies and carbonate sedimentary rocks such as limestone and dolostone. Hot waters derived from the granitic magma are rich in silica, iron, aluminium, and magnesium. These fluids mix in the contact zone, dissolve calcium-rich carbonate rocks, and convert the host carbonate rock to skarn deposits in a metamorphic process called metasomatism. The resulting metamorphic rock may consist of a very wide variety of minerals dependent largely on the original composition of the magmatic fluids and the purity of the carbonate sedimentary rocks.