Limestone is a sedimenatary rock; it consists of about 10% of it, by volume. It comes from the minerals calcite and aragonite, which are both different crystal forms of calcium carbonate. It is mostly made up of the skeletal fragments of marine organisms. Limestone has been used quite commonly in architecture, including the pyramids in Egypt. It is readily available, can easily be cut into blocks or more elaborate shapes, and stands up well to exposure. Please consider our many varieties of limestone, some of which are shown below.