LL Demos & Labs: Rock Profile: Green Obsidian
Yep, green. The green color is due to the fact that the iron rich obsidian, being heated in the absence of oxygen (the trees were buried under 8 feet of ash), were exposed to a reducing environment. When iron is reduced it produces a pale green color. This happened about 900 years ago when Glass Mountain, in northern California, exploded. This not only produced a spectacular display of molten fire bombs, ash, and smoke but also creamed a forest of pine trees. These trees were first blown over, then buried in air fall, and then burned out. It was this last process that produced the intricately beautiful green specimens of obsidian that have only been found in this one place in the world.