I had this one just about ready to go last week and then got sidetracked by a wonderful weekend at the coast with my parents. Without further ado, I present obsidian!
Davis Creek rainbow obsidian. Photo by Kris Rowe and Al Fries at http://www.hand2mouthmining.net/Home_Page.php and image in their ebay store.
We humans owe a lot to this stone, as our ancestors across the world relied on its sharpness before they gained the ability to tame metals. Prehistoric man also enjoyed its dark beauty, and began shaping it for adornment some time before 7000 BCE. It has also been used experimentally for heart surgery, as obsidian blades are smoother and many times sharper than stainless steel, causing less tissue damage and as a result, faster healing.
Obsidian is a natural glass made from the rapid hardening of silica-laden lava. It is usually at least 70% silicon dioxide, but obsidian is technically not a mineral because it does not have a uniform chemical composition or a crystal structure. The cooling of the lava occurs fast enough that the silica polymerizes instead of crystallizes.
Tumbled snowflake obsidian. Image from and stones for sale at http://www.africangems.com/
The white patterns of snoflake obsidian occur when crystals of silicon dioxide are allowed to form, called crystobalite. Elemental impurities give obsidian hints of yellow, brown, blue, and green. A beautiful iridescent or fiery sheen can arise from light bouncing off sheets of trapped air bubbles. My husband and I bought a carved turtle of golden obsidian just like the one below while we were in Mexico, and it appears completely black except when viewed at certain angles.
Gold sheen obsidian turtle. Images from Oak Rocks at http://www.oakrocks.net/servlet/the-7630/Gold-Sheen-Obsidian-2.5/
Obsidian is logically found near areas of volcanic activity, giving it a worldwide but isolated distribution across Europe, Russia, Japan, New Zealand, the Middle East, the U.S., and Mesoamerica. The Mayans were famous users of the black stone. In contrast to jade, which was reserved for the upper class and royalty, all Mayans had access to obsidian, and the material was spread across the empire through trade. They fashioned everyday cutting tools, weapons, jewelry, mirrors, and storage vessels from the glass. It was also important in Armenia, which was both a birthplace of early civilization and is home to some of the finest obsidian deposits. You can walk over Armenian hillsides that are littered with the glistening black glass.
As with most black stones, obsidian is believed to grant protection and dispel negativity. It is also thought to ground a person and let them objectively see who they truly are and what they need to do.