Rocks are naturally occurring solids which are composed of minerals & have been used by humans since ages. From Stone Age, rocks are used for various purposes. Also, the metals and minerals found in rock play an important role in our life. Get to know all the Obsidian Uses. We have provided you with all information about Obsidian rock here. Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock. It is produced when felsic lava extruded from a volcano cools rapidly with minimum crystal growth. Obsidian is available in black, blue, brown, green, orange, red, tan, yellow colors. The streak of a rock is the color of powder produced when it is dragged across an unweathered surface. The streak of Obsidian is white. Get to know more about Obsidian rock and characteristics of Obsidian rock in the next sections.