Obsidian is the result of volcanic lava coming in contact with water. Often the lava pours into a lake or ocean and is cooled quickly. This process produces a glassy texture in the resulting rock. Iron and magnesium give the obsidian a dark green to black color. Obsidian can contain small bubbles of air that are aligned along layers created as the molten rock was flowing before being cooled. These bubbles can produce interesting effects such as a golden (Sheen Obsidian) or a rainbow sheen (Rainbow Obsidian). Obsidian has been used by ancient people as a cutting tool, for weapons, and for ceremonial purposes and is sometimes found by archaeologists. Often confused with smoky quartz, obsidian has similar properties to quartz because of a similar chemistry. However, many properties dependent on a crystal structure are altered or absent in obsidian because it lacks any crystal structure of its own. The piezoelectric and optical properties in quartz are thus absent in obsidian. Smoky quartz usually has a splotchy or zoned distribution to its color while Obsidian is more uniformly distributed.