'Sea of Glass' in the Bible

In front of the throne was what looked like a sea of glass, like crystal. Around the throne, in the middle of each side, were four animals covered with eyes in front and behind.

And I saw what looked like a sea of glass mixed with fire, and standing upon the sea of glass those who had come off victorious from the animal and its statue and the number corresponding to its name. They had harps that God had given them,