| Symbol | SiO₂ (>90%) |
|---|
This is a short overview. For the background — history, value over time and notable mines — see Ganister →
A very hard, fine-grained, silica-rich sandstone found beneath certain coal seams, prized for its ability to withstand extreme heat. Crushed and reformed into silica bricks, it was the standard refractory lining for the furnaces of the iron and steel industry.