Obsidian, Variant (3.5e Equipment)
From D&D Wiki
Obsidian is an igneous rock that forms when molten rock material cools so rapidly that atoms are unable to arrange themselves into a crystalline structure. It is an amorphous material known as a "mineraloid." The result is a volcanic glass with a smooth uniform texture that breaks with a conchoidal fracture. Obsidian is usually an extrusive rock - one that solidifies above Earth's surface. However, it can form in a variety of cooling environments.
Unfortunately, obsidian is also more brittle than iron or steel and is vulnerable to blunt force damage. Obsidian weapons take 1-1/2 times as much damage from being sundered by bludgeoning weapons and from striking hard surfaces.
Obsidian has 20 hit points per inch of thickness and hardness 8.
Weapons made from obsidian cost 50% more than their standard versions. (This may be different depending on the abundance of obsidian in the campaign environment.