This obsidian arrowhead is 5 1/2 by 3 1/4 inches. With its glassy luster, obsidian is a distinctive stone. Obsidian is formed as lava from volcanic eruptions cools within the earth. The speed at which it cools prevents crystallization and the rock forms as solid volcanic glass. Use obsidian to help block negativity of any kind. As a black gemstone, it symbolizes self-control and resilience. Black stones have protective energies in the sense that black is the absence of light, and therefore, can be used to create invisibility.