Silmaril

From LSWiki

Frankly, I have no idea why this is a material. For a variety of reasons, I think whoever originally designed the Elflords was smoking crack. However, it is, and so:

Silmaril is the name of the variety of magickal gem Elflords possess and use to enhance their guild-granted weapons and armor. It is of incomparible value, surpassing durability, and does not occur naturally.

Information about the original Silmarils of Tolkien lore can be found here.