vitreous silica

The skeleton is formed by small crystals and long threads of vitreous silica, cemented together, during life, by protoplasm.

The melting point of vitreous silica cannot be definitely stated.

Vitreous silica is less hard than chalcedony, but harder than felspar.

The density of vitreous silica is very near to that of ordinary amorphous silica.

The rate of expansion of vitreous silica has been studied by H. le Chatelier, and more recently by Callendar.