Easton's Bible Dictionary (1897)
(Ezek. 1:22, with the epithet “terrible,” as dazzling the spectators with its brightness). The word occurs in Rev. 4:6; 21:11; 22:1. It is a stone of the flint order, the most refined kind of quartz. ” The ancients regarded the crystal as only pure water congealed into extreme hardness by great length of time.
Smith's Bible Dictionary (1863)
the representative in the Authorized Version of two Hebrew words.
Hastings' Dictionary of the Bible (1898) & Schaff's Bible Dictionary
CRYS'TAL. Job 28:17. The word here rendered "crystal" is used nowhere else, and is believed to mean "glass," which was made by the ancient Egyptians and highly valued. " Job 6:16; Job 38:29; Ps 147:17. In Eze 1:22, rock-crystal, a stone perfectly transparent and resembling the purest glass, was plainly meant, and there may be reference to the peculiarly dazzling effect of light reflected from its surface. The ancients supposed that this mineral was only "ice congealed by intense cold," and valued it highly for its great beauty. Its transparency is alluded to in Rev 4:6; Rev 21:11; Rev 22:1.
CU'BIT. See Measures.