Cassiterite ranges in color from yellow to black, but it's generally dark. Its Mohs hardness is 6 to 7, and it's a rather heavy mineral. Despite its dark color, it yields a white streak. Cassiterite occurs in crystals like this specimen as well as in brown, banded crusts called wood tin. Because of its hardness and density, cassiterite may collect in placers, where it abrades into dark pebbles called stream tin. This mineral supported the tin industry of Cornwall for thousands of years.