File:Aragonite (Tazouta, Middle Atlas Mountains, Morocco) 6.jpg
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| Description |
English: Aragonite from Morocco.
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 6000 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 carbonate minerals all contain one or more carbonate (CO3-2) anions. Aragonite has the same chemistry as calcite - it is calcium carbonate (CaCO3). However, aragonite has a different molecular structure - the atoms are packed differently. Different minerals having the same chemical formula are called "polymorphs" (another good example is graphite and diamond - both are carbon, C). Unlike calcite, aragonite forms crystals in the orthorhombic class. Many aragonite crystals are acicular (needle-like) or pseudohexagonal. The latter is the result of six orthorhombic prisms growing parallel to each other. The sample seen here is a radiating cluster of pseudohexagonal, cyclic-twinned aragonite masses. Aragonite is slightly harder than calcite, at H=3.5 to 4, occurs in many colors, and easily bubbles in acid. Aragonite is a little bit heavier than calcite, due to closer packing of atoms. Most modern seashells and coral skeletons are composed of the aragonite. Whitish-colored lime sand beaches in the world are aragonitic. Occasionally, "whitings" are seen in shallow, warm ocean environments. Whitings (cloudy, milky seawater) turn out to have numerous tiny, hair-like needles of aragonite. In the rock record, aragonitic or aragonite-rich sediments convert to calcite over time. Cenozoic-aged carbonate sedimentary rocks are often aragonitic. Mesozoic- and Paleozoic-aged carbonates are almost always calcitic. Many ancient fossils have had their aragonitic shells dissolved away. Ancient shells that were originally calcitic are often still well preserved. Locality: Tazouta, southeast of Sefrou & southeast of Fez, Middle Atlas Mountains, northern Morocco Photo gallery of aragonite: www.mindat.org/gallery.php?min=307 |
| Date | |
| Source | https://www.flickr.com/photos/47445767@N05/53541715361/ |
| 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@N05/53541715361. It was reviewed on 26 March 2024 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| current | 16:46, 26 March 2024 | | 2,244 × 1,964 (3.12 MB) | Ser Amantio di Nicolao (talk | contribs) | Uploaded a work by James St. John from https://www.flickr.com/photos/47445767@N05/53541715361/ with UploadWizard |
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