6 and in front of the throne is what seemed to be a sea of glass, 'resembling crystal, while within the space before the throne and round the throne are four Creatures full of eyes' in front and behind.
Bible verses about "crystals" | Twentieth_Century
Revelation 4:6
Revelation 22:1
1 And the angel showed me 'a river of the Water of Life,' as clear as crystal, issuing from the throne of God and of the Lamb,
Revelation 21:11
11 Its brilliance was like that of some very precious stone, like a jasper, transparent as crystal.