File:Forsterite olivine (Sapat Mafic-Ultramafic Unit; Sapat Mine, Pakistan) 2.jpg
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English: Forsterite olivine from Pakistan.
A mineral is a naturally-occurring, solid, inorganic, crystalline substance having a fairly definite chemical composition and having fairly definite physical properties. At its simplest, a mineral is a naturally-occurring solid chemical. Currently, there are over 5600 named and described minerals - about 200 of them are common and about 20 of them are very common. Mineral classification is based on anion chemistry. Major categories of minerals are: elements, sulfides, oxides, halides, carbonates, sulfates, phosphates, and silicates. The silicates are the most abundant and chemically complex group of minerals. All silicates have silica as the basis for their chemistry. "Silica" refers to SiO2 chemistry. The fundamental molecular unit of silica is one small silicon atom surrounded by four large oxygen atoms in the shape of a triangular pyramid - this is the silica tetrahedron - SiO4. Each oxygen atom is shared by two silicon atoms, so only half of the four oxygens "belong" to each silicon. The resulting formula for silica is thus SiO2, not SiO4. The simplest & most abundant silicate mineral in the Earth's crust is quartz (SiO2). All other silicates have silica + impurities. Many silicates have a significant percentage of aluminum (the aluminosilicates). Olivine is a common mineral in many ultramafic igneous rocks. It is magnesium iron silicate - (Mg,Fe)2SiO4. “Olivine” actually refers to a continuous spectrum of chemistries between pure magnesium silicate, Mg2SiO4 and pure iron silicate, Fe2SiO4. Magnesium-rich olivine (forsterite) is more common than iron-rich olivine (fayalite). Olivine is typically greenish-colored - it has a hardness of 7, a conchoidal fracture, a glassy, nonmetallic luster, and a white streak. Pakistan has produced nice, gem-quality olivine ("peridot") for several years. The material comes from the Sapat Olivine Deposit in the western Himalayan Mountains. Olivine crystals are derived from a fault zone where partial serpentinization and recrystallization of dunite peridotites have occurred. The ultramafic host rocks are mid-Cretaceous in age (99 to 105 million years old). Peridot formation in the shear zone postdates that. Host unit: Sapat Mafic-Ultramafic Unit, Kohistan Complex, mid-Cretaceous (99 to 105 Ma) Locality: Sapat Olivine Deposit, mountainside ~19.5 air-kilometers northeast of the town of Naran, North-West Frontier, northeastern Pakistan (vicinity of 35° 02' 54" North latitude, 73° 46' 34" East longitude) Photo gallery of olivine/peridot from this site: www.mindat.org/gallery.php?loc=2536 Photo gallery of olivine: www.mindat.org/gallery.php?min=2983 Some references on Sapat peridot / olivine: Jan et al. (1993) - The Sapat mafic-ultramafic complex, Kohistan arc, North Pakistan. in: Himalayan Tectonics. Geological Society Special Publication 74: 113-121. Jan & Khan (1996) - Petrology of gem peridot from Sapat mafic-ultramafic complex, Kohistan, NW Himalaya. Geological Bulletin of the University of Peshawar 29: 17-26. Khan et al. (2004) - Origin of dunite of the Sapat Complex, Himalaya, North Pakistan. Himalayan Journal of Sciences 2(4): 179. |
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| Source | https://www.flickr.com/photos/47445767@N05/50981094602/ |
| Author | James St. John |
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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/50981094602. It was reviewed on 26 February 2021 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| current | 22:41, 26 February 2021 | | 3,011 × 2,617 (5.67 MB) | Ser Amantio di Nicolao (talk | contribs) | Uploaded a work by James St. John from https://www.flickr.com/photos/47445767@N05/50981094602/ with UploadWizard |
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