There are many types of obsidian found through the world, mahogany, blue sheen, gold sheen, silver sheen, rainbow, midnight lace, Burns green, snowflake, pink lady and others. Many of these types are found in the volcanic domes of the Glass Buttes area of Oregon. This is an area of approximately 35 square miles and is under BLM management.
This type, called fire obsidian, without a doubt is some of the most colorful and most rare of them all. It can rival the very finest of precious opal! In all the world, fire obsidian is only found in Oregon.
Fire obsidian has unique microthin, parallel layers so thin you really have to look hard to see them! Careful cutting and polishing this obsidian, a "fire" layer needs to run close and parallel to the cabs top to bring out the explosion of colors. Best viewed in good lighting, the colors can be every color of the rainbow! Some layers vary in colors. Some finished cabochons will have only one color, others the entire spectrum. Reds, gold's, blue, green purples to name a few.
The colors in this obsidian are caused by microthin layers containing magnetite nano-crystals. No two layers of fire are the same. Some layers reflect many colors in bands and patterns, sometimes sharp boundaries between the colors. Other layers have colors that range from red to green to blue to yellow, similar to an oil sheen on water. Some layers reflect only one color, usually purple or deep red.
James A. Miller has authored a fine article on fire obsidian in the January 2006 issue of Rock and Gem magazine.