It is rare to find obsidian older than about 20 million years, which is very young in comparison to most continental rocks that form the Earth's crust. Obsidian is relatively unstable from a geologic perspective.
The bubbles can be seen readily with a strong magnifying glass or a microscope. Some of these bubbles are visible to the naked eye.
Tiny gas bubbles that have been stretched nearly flat along the flow layers in obsidian generally cause the reflectance of gold sheen and silver sheen obsidian. Very small inclusions of water vapor in the form of bubbles often are trapped in the glass. The reflectance of rainbow obsidian is likely attributed to a preferred orientation of microscopic crystals of feldspar or mica oriented along flow layers.Ī certain amount of water always is present in obsidian. Microscopic crystals of various types of feldspars may yield the unique blue, green, purple or bronze colors associated with rainbow obsidian. Abundant, microscopic crystals of minerals like magnetite, hornblende, pyroxene, plagioclase and biotite, combined with tiny fragments of rock, likely produce the jet-black varieties of obsidian. Red or brown obsidian generally results from tiny crystals or inclusions of hematite or limonite (iron oxide).
Clear varieties of obsidian contain very few opaque impurities or microscopic mineral crystals. Gold Sheen Obsidian.The various colors of obsidian are a result of several factors.
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