'Sea of Glass' in the Bible

and before the throne is a sea of glass like to crystal, and in the midst of the throne, and round the throne, are four living creatures, full of eyes before and behind;

and I saw as a sea of glass mingled with fire, and those who do gain the victory over the beast, and his image, and his mark, and the number of his name, standing by the sea of the glass, having harps of God,