'Sea of Glass' in the Bible

And before the throne was a sea of glass like crystal: and in the midst of the throne, and within the circle of the throne, were four living beings 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 his mark, and over the number of his name standing upon the sea of glass, holding the harps of God.