Crystal
Archimandrite Nikifor’s Biblical Encyclopedia
(Ezek. 1:22)—a transparent or gleaming substance used to describe the awe-inspiring expanse above the living creatures in Ezekiel’s vision. The Hebrew word may refer to ice or crystal; in Job 28:17 it names a precious transparent material compared with gold. Ancient belief sometimes treated rock crystal as permanently frozen ice, but it is a crystalline form of quartz. The visionary comparison communicates brightness, purity, and terrifying splendor rather than a mineralogical definition.