Cassiterite has the composition SnO2, and it contains 78.8% tin. It often contains niobium and tantalum. It belongs to the tetragonal crystal system, and the crystals are equant, prismatic, double cone-shaped, blocky, granular, botryoidal or reniform aggregates. It is waxy yellow, light brown or deep black and has translucent to opaque diaphaneity, an adamantine lustre, greasy fracture surfaces, a specific gravity of 7.0, a Mohs hardness of 6–7 and sub-conchoidal to uneven fractures. It usually coexists with quartz, chalcopyrite and tourmaline in high-temperature hydrothermal veins. The original cassiterite can be transported to placer deposits upon weathering. Cassiterite is the main raw material for smelting tin. Cassiterite crystals can be used as ornamental stones.