Limestone is a sedimentary rock composed of calcium carbonate. It is formed by the accumulation of shells, coral, and other organic material. Oolite is a type of limestone composed of small, rounded grains. DOLOMITE is a type of limestone composed of calcium magnesium carbonate. Calcite is a type of limestone composed of calcium carbonate. MARBLE is a type of limestone that has been metamorphosed and recrystallized. CHALK is a type of limestone composed of the microscopic skeletal remains of marine organisms. Coquina is a type of limestone composed of broken shells and fragments of other materials. Malm is a type of limestone composed of clay and silt-sized particles.