The mineral content of marble is primarily calcite, as well as smaller quantities of quartz, mica and pyrite. Trace minerals of clay or iron oxides in the marble may affect the color of the rock.
During metamorphism, the sedimentary and organic materials found in limestone are chemically altered, resulting in the formation of marble. Exposure to constant heat and pressure cause the calcite crystals in limestone to reform into larger interlocking patterns. The crystals become larger in relation to the length of the metamorphic process. Clay minerals in the marble may also reform into more complex structures and micas as the metamorphic process continues.