Obsidian (/əbˈsɪdi.ən, ɒb-/ əb-SID-ee-ən ob-)[5] is a naturally occurring volcanic glass formed when lava extruded from a volcano cools rapidly with minimal crystal growth.

[6] Produced from felsic lava, obsidian is rich in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium.

An iridescent, rainbow-like sheen (fire obsidian) is caused by inclusions of magnetite nanoparticles creating thin-film interference.

It can be found in Argentina, Armenia, Azerbaijan, Australia,[27] Canada, Chile, Georgia, Ecuador, El Salvador, Greece, Guatemala, Hungary, Iceland, Indonesia, Italy, Japan, Kenya, Mexico, New Zealand, Papua New Guinea, Peru, Russia, Scotland, the Canary Islands, Turkey and the United States.

Obsidian flows which are so large that they can be hiked on are found within the calderas of Newberry Volcano (Big Obsidian Flow,[28] 700 acres) and Medicine Lake Volcano in the Cascade Range of western North America, and at Inyo Craters east of the Sierra Nevada in California.

Yellowstone National Park has a mountainside containing obsidian located between Mammoth Hot Springs and the Norris Geyser Basin, and deposits can be found in many other western U.S. states including Arizona, Colorado, New Mexico, Texas, Utah, and Washington,[29] Oregon[30] and Idaho.

There are only four major deposit areas in the central Mediterranean: Lipari, Pantelleria, Palmarola and Monte Arci (Sardinia).

[36][37][38][39][40] Manufacture of obsidian bladelets at Lipari had reached a high level of sophistication by the late Neolithic, and was traded as far as Sicily, the southern Po river valley, and Croatia.

[42] Anatolian sources of obsidian are known to have been the material used in the Levant and modern-day Iraqi Kurdistan from a time beginning sometime about 12,500 BC.

[43] Obsidian artifacts are common at Tell Brak, one of the earliest Mesopotamian urban centers, dating to the late fifth millennium BC.

[44] Obsidian was valued in Stone Age cultures because, like flint, it could be fractured to produce sharp blades or arrowheads in a process called knapping.

Through trade, these artifacts ended up in lands thousands of kilometers away from the original source; this indicates that they were a highly valued commodity.

[45] John Dee had a mirror, made of obsidian, which was brought from Mexico to Europe between 1527 and 1530 after Hernando Cortés's conquest of the region.

[46] In the Ubaid in the 5th millennium BC, blades were manufactured from obsidian extracted from outcrops located in modern-day Turkey.

Neutron activation analysis (NAA) on the obsidian found at this site helped to reveal trade routes and exchange networks previously unknown.

A careful analysis of obsidian in a culture or place can be of considerable use to reconstruct commerce, production, and distribution, and thereby understand economic, social and political aspects of a civilization.

[55] Similar tracing techniques have also allowed obsidian in Greece to be identified as coming from Milos, Nisyros or Gyali, islands in the Aegean Sea.

The complexity of the production technique for these tools, and the care taken in their storage, may indicate that beyond their practical use they were associated with prestige or high status.

[59] Obsidian was also used on Rapa Nui (Easter Island) for edged tools such as Mataia and the pupils of the eyes of their Moai (statues), which were encircled by rings of bird bone.