Here's why:
* Sharp Edges: Obsidian forms from rapidly cooled volcanic lava, resulting in a glassy, amorphous structure. This lack of crystal structure makes it incredibly brittle and prone to fracture with very sharp edges.
* Durability: Despite its brittleness, obsidian is surprisingly durable and can be used to create sharp tools that last for a long time.
* Historical Use: Obsidian has been used to make tools by humans for thousands of years, with archaeological evidence dating back to the Stone Age.
While other igneous rocks can be used to make tools, obsidian's unique properties make it particularly well-suited for creating sharp and durable cutting and scraping tools.