sil·i·ca 
(sĭlĭ-kə)
(sĭlĭ-kə)n.
A white or colorless crystalline compound, SiO2, which in the form of quartz and certain other minerals is a chief component of the earth's crust. Silica sand is used in making a wide variety of materials, such as glass and concrete.
[New Latin, from Latin silex, silic-, hard stone, flint.]