silica

(SILL-uh-kuh): A substance found in rocks, sand, and quartz as well as some workplaces.

Silicon dioxide (SiO₂). Note 1: Silica may occur in crystalline or amorphous form, and occurs naturally in impure forms such as quartz and sand. Note 2: Silica is the basic material of which the most common communication-grade optical fibers are presently made. [After FAA]