In geology, marble is the rock formed when limestone undergoes metamorphism.
Heat, pressure, and chemically active fluids recrystallize the calcite or dolomite grains in limestone. The resulting marble is usually more crystalline and harder than its original sedimentary parent rock, although it remains composed mainly of carbonate minerals.
Pure marble is commonly white, while impurities can produce gray, green, pink, brown, or black colors. Its ability to take a polish has made it important in sculpture, architecture, and decorative stonework since antiquity.
Marble is different from quartzite, which forms from sandstone, and slate, which commonly forms from shale. Acid can fizz on many marbles because their carbonate minerals react with dilute hydrochloric acid.