Onyxite

Onyxian Glass, known as Onyxite  Is a valuable, transparent but very durable material, often mistaken with glass. It is special for its hardness. For instance dropping a 1 kilogram piece of steel from ten metres on a sheet of Onyxite wont leave a single scratch or internal crack.

Photonic polarization
It is used as eye protection from excesive light without the need of shading the visibility. The master smiths have glasses made off Onyxite in order to shield themselves from the light during the extreme temperature smithing and smelting.