A chemical element, symbol Si, atomic number 14, and atomic weight 28.086. Silicon is the most abundant electropositive element in the Earth's crust. The element is a metalloid with a decided metallic luster; it is quite brittle. It crystallizes in the diamond lattice, has a specific gravity of 2.42 at 20°C (68°F), melts at 1420°C (2590°F), and boils at 3280°C (5940°F). The element is usually tetravalent in its compounds, although sometimes divalent, and is decidedly electropositive in its chemical behavior. In addition, pentacoordinate and hexacoordinate compounds of silicon are known.