What is mineral glass?

The chemical description of mineral glass is silicon oxide SiO2. Adding other oxides (alumina or boric oxide) this simple “window glass” can be refined. “Hardlex” (Seiko) is an example for a trade mark for refined mineral glass. Mineral glass is significantly harder than acrylic glass, they are nonosmotic and not yellowing.

However, even mineral glass can be damaged if somebody scratches it unintentionally against a stone wall. Mineral glasses cannot be polished easily, a replacement glass will be by far the most economical option. Unfortunately mineral glass can break and in a worst-case-scenario small glass splinters could eventually damage the movement.

Good mineral glass is not simple “window glass”. Good quality mineral glass gets hardened in a laborious chemical procedure. Monitoring the ion exchange precisely during the fabrication of mineral glass, the surface tension is improved and makes it more impact-resistant and  projectile effects of any rupture can be reduced.

Source: wikipedia