The composition of borosilicate glass is approx. 80% SiO2 ("silica"), approx. 10% B2O3 ("boric trioxide”), and approx. 10% other minerals (Al2O3, K2O, CaO, MgO). Borosilicate has a very high chemical and thermal resistance. Borosilicate is used for vacuum chambers and windows of plasma chambers which need to be resistant to etching attacks.