Obsidian

Obsidian is an extrusive igneous rock. It is occurring as a natural glass formed by the rapid cooling of viscous lava from volcanoes. Result of this formed, glass occupies more than 80 % and that have seeming conchoidal fracture and vitreous luster. It usually colours dark, black, grey-black to grey. Also It occur red, brown-green, green, yellow and rare transparent colourless.

Colour is controlled factor by trace element content and the character of inclusion. Hand-specimen rock is common combination of two colours. Those are combination of black and brown colours. The name obsidian is very old. It is ascribed to Theophrastus who used it for the first time in 320 BC.

The translation into English of Natural History written by Pliny the Elder of Rome shows a few sentences on the subject of a volcanic glass called obsidian (lapis obsidianus), discovered in Ethiopia by Obsidius Obsidian is treasured for its unique appearance and sharp edges, which have made it valuable to humans for thousands of years in toolmaking, art, and cultural practices. The manufacture of obsidian tools by humans dates back to the Stone Age. At some locations, tons of obsidian flakes reveal the presence of ancient "factories." Some of these sites have enough waste debris to suggest that many people labored there for decades producing a variety of obsidian objects. Making arrowheads, spear points, knife blades, and scrapers from obsidian, chert, or flint might have been the world's first "manufacturing industry."

Obsidian is primarily composed of silicon dioxide (SiO2), which is the same chemical composition as quartz, but it has a completely different structure due to its rapid cooling from a molten state. The chemical composition of obsidian is approximately 70-75% SiO2. However, it can contain various impurities and trace elements that give rise to its different colors and varieties. Although most rocks that form in the Earth’s crust are very old, obsidian is rarely older than 20 million years old which is young for a rock. Significant deposits of obsidian are found in Argentina, Canada, Chile, Ecuador, Greece, Guatemala, Hungary, Iceland, Indonesia, Italy, Japan, Kenya, Mexico, New Zealand, Peru, Russia, United States, and many other locations.