(Chemical symbol Sn). An element of atomic number 50, atomic weight 118.69, mp 231.8C, specific gravity (grey) 5.75, (white) 7.31. A soft, white, lustrous metal obtained almost entirely from the mineral cassiterite, SnO2. Tin is not affected on exposure to air at ordinary temperatures. At temperatures above 13.2C the white tetragonal allotropic form is stable and below this the grey cubic form may exist. Above 170C, tin is rhombic in crystal structure. The metal has low tensile strength and hardness but good ductility.