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 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 and pure crystal 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.”—Rev. 4:6; 21:11; 22:1; see JEWELS AND PRECIOUS STONES.