Marble is a metamorphic rock formed from limestone. Changes in the limestone's chemical properties due to external forces can result in the creation of marble.
Metamorphic rocks are produced when the properties of existing rocks are changed through contact with heat or pressure. Marble is formed when the mineral calcite, which is found in limestone, recrystallizes due to exposure to magma or regional metamorphism. Marble is composed primarily of interlocking calcite crystals, mica and quartz. The length of the metamorphic process the limestone undergoes determines the size of the reformed calcite crystals in the newly formed marble. The majority of the sedimentary and fossil content in the limestone is altered or replaced during the metamorphic process.