May or may not be the same as Obsidian.
A variety of weapons made by obsinite
Obsinite is the term used by outsiders for a form of rock or volcanic glass used as tools by the Lizardmen of Lustria. Neither the metallurgists of the Imperial College of Engineering nor the wizards of the Golden Order in Altdorf have been able to truly identify what kind of material obsinite really is.[1a]
Obsinite appears to be some form of super-hardened stone, yet it is not brittle or fragile like the stone weapons of other crude, warm-blooded races. The secrets of the manufacture of obsinite have thus far remained hidden from the jealous eyes of strangers, guarded carefully by the caste of Skink artisan-priests responsible for constructing the weapons. Indeed, it is said to be more durable even than the highest quality steel and capable of smashing any armour it strikes.[1a]