Obsidian is a mineral we sometimes call volcanic glass, and like "regular" glass, it is composed of mostly silicon dioxide (SiO 2 ). Some oxides of magnesium and iron are usua…lly present, and these will cause the color and appearance, and some of its other physical characteristics, to vary. Like glass, obsidian has no crystal structure but could be looked as a supercooled liquid. It is in many other ways similar to glass, and its specific gravity is about 2.6 and its hardness usually ranges between 5 and 5.5 on the Mho's Scale..
Volcanic glass has volcanic origins, as its name implies, and it is widely distributed in different locations around the world. It can be uncovered in small digs or, in some cases, walked on in vast fields of cooled and solidified volcanic flows in Europe, Asia, Africa and the Americas. Alaska, Hawaii and a number of western states in the U.S. list it among their mineral resources, though its demand is based on current use as a specimen material for rock collectors, and as a raw material for the manufacture of jewelry or other objects..
Obsidian was used by primitive peoples in many places around the world to make points for weapons and edges for tools, and it was prized for this application. It was a critical element for survival of these clever crafters of the edges that brought animals to the ground and allowed the processing for food, clothing and other applications. It is from ancient records that it has acquired its name. Specifically, it comes from the ancient work called Natural History by Pliny. He called it "Obsidianus" because it resembled an Ethiopian stone named by Obsius..
A link can be found below for more information, and it will take the curious investigator to the Wikipedia post on obsidian. It's a well-written and easy-to-read article, and it's definitely worth the few minutes it will take to review it. 1. it usually appears black. 2. it is an extrusive igneous rock therefore it is volcanic. 3. it is shiny and glassy. etc. (MORE)