2.46 · Natural Substances · Precious and Semiprecious Stones and Substances

crystal a very hard, translucent, and usually transparent type of quartz The equivalent of ‘crystal’ is often a descriptive phrase such as ‘a brilliant stone’ or ‘a shining stone’ or ‘a glass-like stone.’ In developing a satisfactory term for crystal, it is important to avoid possible confusion with diamond.
Some scholars, however, interpret κρύσταλλος in REV 4:6 as being a reference to ice (see 2.11).

REV 4:6

2.11 · Natural Substances · Water

ice frozen water In both REV 4:6 and REV 22:1 (the only two passages in which κρύσταλλος occurs in the NT) the meaning may, however, be ‘rock crystal’ rather than ‘ice’ (see 2.46).
Though in the Arctic regions people may have a number of different terms for various kinds and forms of ice, there are many areas in the world in which there is no existing local term for ‘ice.’ Sometimes a descriptive phrase such as ‘hardened water’ is employed, and in a number of languages a term is simply borrowed from a dominant language of the region. However, in REV 4:6 and REV 22:1 it is possible to focus upon the brilliance of color rather than the particular substance and thus to speak of λαμπρὸς ὡς κρύσταλλος as ‘that which is sparkling white’ or ‘... bright white.’

REV 4:6 · REV 22:1