'Glassy' in the Bible

and in front of the throne there was something like a sea or large expanse of glass, like [the clearest] crystal. In the center and around the throne were four living creatures who were full of eyes in front and behind [seeing everything and knowing everything that is around them].

Then I saw something like a sea or large expanse of glass mixed with fire, and those who were victorious over the beast and over his image and over the number corresponding to his name were standing on the sea or large expanse of glass, holding harps of God [worshiping Him].