from kruos, "ice," and hence properly anything congealed and transparent, denotes "crystal," a kind of precious stone, Revelation 4:6; 22:1 . Rock crystal is pure quartz; it crystallizes in hexagonal prisms, each with a pyramidical apex.
"to be of crystalline brightness and transparency, to shine like crystal," is found in Revelation 21:11 , where it is said of Christ as the "Light-giver" (phoster) of the Heavenly City (not phos, "light," RV and AV). Possibly there the verb has a transitive force, "to transform into crystal splendor," as of the effect of Christ upon His saints.
With over 3,400 entries, this timeless classic is THE reference guide to New Testament Greek words for English readers. It explains the meaning of the original Greek with the added dimension of the context of the Greek word.Wikipedia
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