Obsidian

Obsidian
Obsidian
General
Category	Volcanic glass
Identification
Color	usually black; sometimes green or brown; rarely yellow, orange, red or blue
Fracture	Conchoidal
Mohs scale hardness	5–6
Luster	Vitreous
Specific gravity	c. 2.4
Optical properties	Translucent
Other characteristics	Texture: Smooth; glassy
References

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. It is an igneous rock.^[6]

Obsidian is produced from felsic lava, rich in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. It is commonly found within the margins of rhyolitic lava flows known as obsidian flows. These flows have a high content of silica, granting them a high viscosity. The high viscosity inhibits diffusion of atoms through the lava, which inhibits the first step (nucleation) in the formation of mineral crystals. Together with rapid cooling, this results in a natural glass forming from the lava.^[7]

Obsidian is hard, brittle, and amorphous; it therefore fractures with sharp edges. In the past, it was used to manufacture cutting and piercing tools, and it has been used experimentally as surgical scalpel blades.^[8]

^ King, Hobart M. "Obsidian". Geology.com. Retrieved 3 February 2023.
^ Peter Roger Stuart Moorey (1999). Ancient Mesopotamian Materials and Industries: the archaeological evidence. Eisenbrauns. pp. 108–. ISBN 978-1-57506-042-2.
^ Ericson, J.E.; Makishima, A.; Mackenzie, J.D.; Berger, R. (January 1975). "Chemical and physical properties of obsidian: a naturally occurring [sic] glass". Journal of Non-Crystalline Solids. 17 (1): 129–142. Bibcode:1975JNCS...17..129E. doi:10.1016/0022-3093(75)90120-9.
^ Obsidian, Mindat.org
^ "obsidian". Dictionary.com Unabridged (Online). n.d.
^ Rafferty, John P. (2012). Rocks (1st ed.). New York, NY: Britannica Educational Pub. in association with Rosen Educational Services. p. 97. ISBN 9781615304929.
^ Raymond, Loren A. (1995). Petrology : the study of igneous, sedimentary, metamorphic rocks. Dubuque, IA: Wm. C. Brown. p. 27. ISBN 0697001903.
^ Brian Cotterell; Johan Kamminga (1992). Mechanics of pre-industrial technology: an introduction to the mechanics of ancient and traditional material culture. Cambridge University Press. pp. 127–. ISBN 978-0-521-42871-2. Retrieved 9 September 2011.

[Geolcom-1] King, Hobart M. "Obsidian". Geology.com. Retrieved 3 February 2023.

[2] Peter Roger Stuart Moorey (1999). Ancient Mesopotamian Materials and Industries: the archaeological evidence. Eisenbrauns. pp. 108–. ISBN 978-1-57506-042-2.

[3] Ericson, J.E.; Makishima, A.; Mackenzie, J.D.; Berger, R. (January 1975). "Chemical and physical properties of obsidian: a naturally occurring [sic] glass". Journal of Non-Crystalline Solids. 17 (1): 129–142. Bibcode:1975JNCS...17..129E. doi:10.1016/0022-3093(75)90120-9.

[4] Obsidian, Mindat.org

[5] "obsidian". Dictionary.com Unabridged (Online). n.d.

[6] Rafferty, John P. (2012). Rocks (1st ed.). New York, NY: Britannica Educational Pub. in association with Rosen Educational Services. p. 97. ISBN 9781615304929.

[7] Raymond, Loren A. (1995). Petrology : the study of igneous, sedimentary, metamorphic rocks. Dubuque, IA: Wm. C. Brown. p. 27. ISBN 0697001903.

[8] Brian Cotterell; Johan Kamminga (1992). Mechanics of pre-industrial technology: an introduction to the mechanics of ancient and traditional material culture. Cambridge University Press. pp. 127–. ISBN 978-0-521-42871-2. Retrieved 9 September 2011.

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