“The rock forming the earth’s crust falls into three generic groups: igneous, sedimentary and metamorphic. Heat, pressure, and chemical reactions may change either igneous or sedimentary rock into metamorphic rock, meaning ‘changed in form’ usually into more compact and crystalline condition, and even metamorphic rocks may be further altered to higher ranks of metamorphism. Rocks may become plastic under great pressure and high temperature and by earth movement. They may be folded into complex forms with a banded structure. Many Constituent minerals may be dissolved, transported, and reprecipitated by thermal waters. Heat and pressure may cause recrystallization.

Marble is, therefore, metamorphic rock resulting from the recrystallization of limestone. Commercially, however: all calcareous rocks produced by nature and capable of taking a polished are called marble, as are some dolomitic and serpentine rocks.”

- Marble Institute of America