As used in the Bible, crystal denotes a clear, transparent mineral, probably the variety of quartz presently called rock crystal. Rock crystal is quartz in its purest form, composed of silicon and oxygen. It is found in its characteristic six-sided form in nearly all kinds of rock and is colorless, clear, and glassy in appearance. Rock crystal is much harder than other common minerals, and it is sometimes cut for gemstones.

The comparative worth of “rock crystal” (Heb., ga·vishʹ) in Job’s day may be suggested by his appraisal of it along with coral and pearls, and yet he considered them all to be of less value than wisdom. (Job 28:18) Revelation uses clear, brilliant, pure crystal (Gr., kryʹstal·los) to describe “a glassy sea like crystal,” the radiance of the holy city, New Jerusalem, as “a jasper stone shining crystal-clear,” and “a river of water of life, clear as crystal.”​—Re 4:6; 21:11; 22:1.