Limestone is mostly made of calcite and dolomite; the former is composed or calcium, carbon and oxygen, while the latter is composed of calcium and magnesium. Depending on the type of limestone, other minerals and elements may be included.
In order for a rock to be limestone in a geological sense, it must contain at least 50 percent calcite and dolomite combined and 50 percent or less of other elements. Commercial limestone contains 80 percent calcite and dolomite and 20 percent other elements.
Limestone can be categorized into different kinds. Calcite limestone has more than 90 percent calcite and at least 10 percent dolomite, while dolomitic limestone must contain 10 to 50 percent dolomite and calcitic limestone must have 10 to 50 percent calcite. Limestone containing more than 90 percent dolomite is dolomite limestone.