A nonmetallic element occurring extensively in the earth's crust in silica and silicates, having both a brown amorphous and a gray lustrous crystalline allotrope, and used doped or in combination with other materials in glass, semiconducting devices, concrete, brick, refractories, pottery, and silicones. Atomic number 14; atomic weight 28.086; melting point 1,414°C; boiling point 3,265°C; specific gravity 2.33 (25°C); valence 2, 4. See Periodic Table.