Obsidian is naturally occurring volcanic glass which has been used to make blades and tools for thousands of years. More recently it is used for gemstones and other carved ornaments. Obsidian forms in cooling lava. Obsidian is not considered to be a true mineral because its composition is too complex and it does not have a crystalline structure. In its pure form, obsidian has a dark body color due to the presence of iron and magnesium. Obsidian comes in a number of different verities. Some of the basic verities are Just plain Black, Mahogany which is black with reddish bands. The Mahogany may also have a gold sheen to it when turned in bright light and is called Gold Sheen. Silver sheen and rainbow are 2 more verities. The rainbow has multiple colors. Black & White Snowflake is popular in jewelry. There is a light gray body color with dark lines and swirls running through it, called Midnight Lace. There is green obsidian and fire obsidian. Nodules from California called Peacock have very bright color sheen and small nodules from Arizona are called Apache Tears.