It is a naturally occurring volcanic glass which has been used as a gemstone since ancient times. Obsidian was named after Obsius, a Roman civilian who had discovered a similar stone. Obsidian forms when lava cools and whilst it is mineral-like, it is not considered to be a true mineral because its composition is too complex and it does not have a crystalline structure, it takes the shape of the cavity where it cools down. Obsidian can be identified by its glassy lustre and single refraction. Obsidian is found in places that have experienced volcanic eruptions. Such places include Argentina, Armenia, Azerbaijan, Canada, Chile, Georgia, Greece, El Salvador, Guatemala, Iceland, Italy, Japan, Kenya, Mexico, New Zealand, Peru, Scotland, Turkey and the United States. In addition to its decorative use, obsidian has a practical use. Due to its lack of cleavage, conchoidal fracture and acute edges when broken, it has been used to make smooth and sharp surgical scalpel blades. Obsidian has been used to make arrow heads and blades, as well as ornaments for thousands of years by people such as the pre-Columbian Mesoamericans and the ancient Egyptians.
In its pure form, obsidian has a dark body colour due to the presence of iron and magnesium. Obsidian can be classified into types according to a variety of characteristics. However, some basic types of obsidian include the following: Mottled (snowflake and peanut obsidian), banded or veined (Mahogany, midnight lace and pumpkin obsidian), pebbles or small nodules (Apache tears) and sheen (sheen obsidian, cat's eye, rainbow and fire/flame obsidian).
Due to the opacity of most types of obsidian, it is usually cabochon cut, fancy cut, sphere-cut, tumbled, made into cameos or carved. Cabochon cuts also best exhibit any sheen or iridescence. Translucent to transparent materials are faceted.
Obsidian is not usually treated or enhanced in any way.