Obsidian

World of Darkness - Armory

Obsidian is the result of hardened lava, generally flowing from a volcano, creating a type of glass that a number of native groups used in their weapons. When one applies light pressure to the stone, it chips away and fragments into a very sharp edge. Generally, indigenous peoples craft the stone into knives or swords (using other natural items like antlers, horns or wood for handles). Some use them as arrow-tips, as well. The stone is generally a deep shade of black, though some obsidian is red or brown, depending on what other materials (like hematite or oxides) were present when the lava hardened.
Obsidian is light and features a dire edge. Any weapon made of obsidian grants the wielder a +2 to attack. Like glass, obsidian can slice through soft materials (like flesh) as if they were little more than air. Unfortunately, obsidian is also notoriously brittle. This is reflected in the material’s Durability of 1, as obsidian is only as strong as thick glass. In addition, if using the optional blade sharpening rule below, obsidian weapons can’t benefit, as attempts to sharpen these weapons further merely chip the material away.
Weapons of obsidian aren’t easy to find. Most of them are in museums, though anyone can attempt to craft an obsidian blade using a Dexterity + Crafts roll (but pressing the rock against any hard surface will cause it to flake and break).

Type

Rock