'Sea of Glass' in the Bible

also in front of the throne there is like a sea of glass, resembling crystal. And on each side of the throne, all round it, four living Creatures full of eyes inside and outside;

And I saw what was like a sea of glass mixed with fire, and, standing beside the sea of glass, those who came off conquerors from the Beast and his statue and the cipher of his name; they had harps of God