An elementary substance found as an oxide in the mineral
   cassiterite, and reduced as a soft white crystalline metal, malleable
   at ordinary temperatures, but brittle when heated. It is not easily
   oxidized in the air, and is used chiefly to coat iron to protect it
   from rusting, in the form of tin foil with mercury to form the
   reflective surface of mirrors, and in solder, bronze, speculum metal,
   and other alloys. Its compounds are designated as stannous, or stannic.
   Symbol Sn (Stannum). Atomic weight 117.4.