File:Chiastolite andalusite (Precambrian; Keivy area, Russia) 1 (34576177802).jpg
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Summary
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| Description |
Andalusite from the Precambrian of Russia. 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 5400 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). Andalusite is an aluminum silicate mineral, Al2SiO5. This chemical occurs as three different polymorphs - andalusite, kyanite, and sillimanite. Andalusite is a metamorphic mineral. It has a nonmetallic luster and varies in color, but always has a white streak. It is hard (H = ~7) and has cleavage. Chiastolite is a variety of andaulsite having dark-colored inclusions that result in a flower-like, tetraradiate structure. Locality: unrecorded/undisclosed site in the "Keivy" area, Kola Peninsula, far-northwestern Russia Photo gallery of andulasite and chiastolite: <a href="https://www.mindat.org/gallery.php?min=217" rel="noreferrer nofollow">www.mindat.org/gallery.php?min=217</a> and <a href="https://www.mindat.org/gallery.php?min=1001" rel="noreferrer nofollow">www.mindat.org/gallery.php?min=1001</a> |
| Date | |
| Source | Chiastolite andalusite (Precambrian; Keivy area, Russia) 1 |
| 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@N05/34576177802 (archive). It was reviewed on 5 December 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| Date/Time | Thumbnail | Dimensions | User | Comment | |
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| current | 13:34, 5 December 2019 | | 1,007 × 1,194 (911 KB) | Ser Amantio di Nicolao (talk | contribs) | Transferred from Flickr via #flickr2commons |
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