Crystal
In Ezekiel 1:22, this signifies the spiritual divine in heaven. (Apocalypse Explained 931[2])
In Revelation 22:1, this signifies divine truth shining from interior good. (Apocalypse Explained 253[4])
In Revelation 4:6, this signifies the new heaven which is constituted by Christians who had been in general truths from the literal sense of the Word. (Apocalypse Revealed 238)
Revelation 22:1
1
He showed me a river of water of life, clear as crystal, proceeding out of the throne of God and of the Lamb,