Alleged to help connect to the ancient warrior within yandou reclaim forgotten abilities you learned in past lives.
Obsidian is actually a type of glass and is literally lava that cooled from its molten form so quickly, there was not time for any crystals to form. The actual composition of the rock is dependent on what minerals, gases, and such were in the immediate area when the lava cooled.
Since ancient times, obsidian has been used in making various tools. In times past, arrowhead, knives, and saws for cutting animals were made from it. Today, some of the best scalpels in the world or made from it because of how thinly and smoothly the blade can be sharpened.