Obsidian: is a type of naturally-occurring glass that results when volcanic lava flow cools rapidly before crystallization forms. Because of it’s lack of crystallization, it is considered a mineraloid, or type of natural glass, rather than a true mineral. Pure Obsidian is usually dark or black in appearance, though the color varies depending on the presence of impurities. Obsidian was revered by ancient cultures. It was one of the major barter materials and prized for its ability to be worked to razor-sharp edges for arrows and spears. It has been used since prehistoric times for making tools, masks, weapons, mirrors and jewelry.