LEARN ABOUT OBSIDIAN 🖤 Obsidian is an igneous rock consisting mainly of silicon dioxide, which occurs as a natural glass. It is formed during the eruption of Felsic lava from volcanoes. Because of the high concentration of silica within Felsic lava, the high viscosity coupled with the rapid cooling upon it’s expulsion from the earth inhibits the formation of mineral crystals, allowing instead for a natural glass to form from the lava. The structures that we find within crystalline forms simply