Why is the ninth month called September?
"silicon dioxide," 1756, from German Quarz, Zwarc "rock crystal," from Middle High German twarc, probably from a West Slavic source, cf. Czech tvrdy, Polish twardy "quartz," noun uses of an adjective meaning "hard," from Old Church Slavonic tvrudu "hard," from Proto-Slavic *tvrd-, from PIE *(s)twer- "to grasp, hold; hard."
A very hard crystalline form of silicon dioxide used in chemical apparatus and in optical and electric instruments.
A hard, transparent trigonal mineral that, after feldspar, is the most common mineral on the surface of the Earth. It occurs as a component of igneous, metamorphic, and sedimentary rocks as well as in a variety of other forms such as rock crystal, flint, and agate. Some crystalline forms, such as amethyst, are considered gemstones. Chemical formula: SiO2.