File:Tourmaline in pegmatite (Precambrian; White Elephant Mine, Black Hills, South Dakota, USA).jpg
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[edit]DescriptionTourmaline in pegmatite (Precambrian; White Elephant Mine, Black Hills, South Dakota, USA).jpg |
English: Tourmaline in pegmatite from the Precambrian of South Dakota, USA.
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 5900 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. Tourmaline is a classic "garbage-can mineral" - it has a little bit of just about everything. Tourmaline can be given the formula (Na,Ca)(Li,Mg,Al)(Fe,Mn,Al)6(BO3)3(Si6O18)(OH,F)4 - sodium calcium lithium magnesium iron manganese hydroxy-fluoro-boro-aluminosilicate. Tourmaline has a nonmetallic luster, varies in color but is often blackish, has a white streak, is quite hard (H = 7 to 7.5), frequently has elongated crystals with subtriangular cross-sections and striated faces, no cleavage, and conchoidal fracture. Tourmaline is a group of minerals, the most common of which is the blackish-colored, Fe-rich schorl. Other varieties include achroite, dravite (= Mg-rich), elbaite (= Li & Na-rich), indicolite, liddicoatite (= Li & Ca-rich), rubellite, verdelite, and others. The latter-listed tourmalines are often richly colored (greenish, yellowish, reddish, pinkish, bluish, multicolored). Tourmaline is moderately common in pegmatites and some metamorphic rocks. It can even be rock-forming - see the scarce rock tourmalinite (www.flickr.com/photos/jsjgeology/15095512541). The black material in the rock seen here is schorl tourmaline. The host rock is pegmatite, or pegmatitic granite. Pegmatites are very coarsely-crystalline textured, intrusive igneous rocks. Their large crystal size is the result of cooling of water-rich magma. Pegmatites often have concentrations of unusual elements, which is conducive to the formation of less common minerals such as uraninite, beryl, and tourmaline. Locality: White Elephant Mine, southern Black Hills, western South Dakota, USA Photo gallery of tourmaline: www.mindat.org/gallery.php?min=4003 |
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Source | https://www.flickr.com/photos/47445767@N05/52796914226/ |
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@N05/52796914226. It was reviewed on 7 April 2023 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
7 April 2023
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current | 17:13, 7 April 2023 | ![]() | 3,728 × 2,218 (7.98 MB) | Ser Amantio di Nicolao (talk | contribs) | Uploaded a work by James St. John from https://www.flickr.com/photos/47445767@N05/52796914226/ with UploadWizard |
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Date and time of data generation | 08:29, 2 April 2023 |
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File change date and time | 00:59, 6 April 2023 |
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Date and time of digitizing | 08:29, 2 April 2023 |
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Date metadata was last modified | 20:59, 5 April 2023 |
Unique ID of original document | E5BBE95CE83C08ECF90A89F94155DD6A |
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