In Latin, mirror stone. They also say glass, light stone, glitter, crystalline plaster. As Pliny the Elder tells us in his Natural History the best mines of this crystallized gypsum were in the surroundings of Segóbriga, near the current Saelices in the province of Cuenca. In the first centuries of our era it was used mainly as glass for windows that although it was not transparent, it was at least translucent.