A strong, low-density, highly corrosion-resistant, lustrous white metallic element that occurs widely in igneous rocks and is used to alloy aircraft metals for low weight, strength, and high-temperature stability. Atomic number 22; atomic weight 47.87; melting point 1,668°C; boiling point 3,287°C; specific gravity 4.51; valence 2, 3, 4. See Periodic Table.