'Sea of Glass' in the Bible

And before the throne there was a sea of glass, like crystal. And in the midst of the throne, and round about the throne, were four living creatures full of eyes before and behind.

And I saw, as it were, a sea of glass mingled with fire, and those who had obtained the victory over the beast, and over his image, and over the number of his name, standing on the sea of glass, having the harps of God.