Strong’s Greek
G2930 — krustallos
The entry below is Strong’s own definition (1890, public domain), and every verse where the word occurs.
κρύσταλλος
krustallos — pronounced kroos'-tal-los
from a derivative of kruos (frost); ice, i.e. (by analogy) rock "crystal":--crystal.
2 occurrences in the KJV.
Revelation 4:6
And before the throne there was a sea of glass like unto crystal: and in the midst of the throne, and round about the throne, were four beasts full of eyes before and behind.
Revelation 22:1
And he shewed me a pure river of water of life, clear as crystal, proceeding out of the throne of God and of the Lamb.