From D&D Wiki
|This material is published under the OGL|
Mundane crystal can be used in place of metal in weapons or armor, using a special forging process. The fortified crystal possesses the properties of a similar masterwork steel weapon or armor, except for visual appearance.
Weapons and armor made of mundane crystal cost the same amount to make as their masterwork counterparts. Any item could potentially be made with mundane crystal. Because mundane crystal armor is considered to be made out of metal, druids cannot wear it.
Mundane crystal properly forged has 25 hit points per inch of thickness and a hardness of 8.