Skarn metamorphic rock. Skarn rocks are formed when igneous or sedimentary rocks are chemically altered by changes in heat and pressure conditions. They are largely composed of calcium, magnesium and iron silicate minerals. The pink skarn in this sample is a breccia, a rock with fragments of one material (dark specks) cemented within a matrix of a different material. These fragments were probably incorporated during the high-intensity phases of metamorphosis when the rock was highly mobile. This sample measures 200 millimetres across.