Limestone Powder Limestone Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO3).Limestone often contains variable amounts of silica in the form of chert (chalcedony, flint, jasper, etc.) or siliceous skeletal fragment (sponge spicules, diatoms, radiolarians), and varying amounts of clay, silt and sand (terrestrial detritus) carried in by rivers.