Obsidian
| Obsidian | |
|---|---|
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| General | |
| Category | Volcanic glass |
| Formula (repeatin unit) | 70–75% SiO2, plus MgO, Fe3O4 |
| Identification | |
| Colour | Deep black |
| Fractur | Conchoidal |
| Mohs scale haurdness | 5–6[1] |
| Skinkle | Vitreous |
| Speceefic gravity | ~2.4[2] |
| Optical properties | Leamin |
| References | [3] |
Obsidian is a naiturally occurrin volcanic gless furmed as an extrusive igneous rock.
It is produced whan felsic lava extrudit frae a volcano cuils swith wi meenimum creestal growthe. Obsidian is commonly foond athin the mairgins o rhyolitic lava pirrs kent as obsidian flows, whaur the chemical composeetion (heich silica content) induces a heich viscosity an polymerisation degree o the lava. The inhibeetion o atomic diffusion throu this heich viscous an polymerised lava explicates the lack o creestal growthe. Obsidian is haird an brickle; it fracturs wi vera jaggie rands, that haed been uised in the past in cuttin an piercin tuils, an haes been uised experimentally as surgical scalpel blads.[4]
References
[eedit | eedit soorce]- ↑ Peter Roger Stuart Moorey (1999). Ancient mesopotamian materials and industries: the archaeological evidence. Eisenbrauns. pp. 108–. ISBN 978-1-57506-042-2.
- ↑ Geological Survey (U.S.) (1981). Geological Survey (U.S.). The Survey. pp. 185–.
- ↑ Obsidian. Mindat.org
- ↑ 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.