File:Dolomite after halite (north of Orion, Major County, Oklahoma, USA).jpg
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| Description |
English: Dolomite pseudomorph after halite from Oklahoma, 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 5200 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. Dolomite is a calcium magnesium carbonate - CaMg(CO3)2. Many ancient rock units (dolostones) were long known to be composed of dolomite. Strangely, dolomite couldn't be found forming in modern oceans. Modern seas do precipitate aragonite, a calcium carbonate mineral. Cores drilled on coral atolls show that dolomite occurs at depth, below beds composed of calcite (= hexagonal CaCO3), which in turn occur at depth below beds composed of aragonite (= orthorhombic CaCO3). Dolomite appears to form principally by the addition of Mg to pre-existing limestones (rocks composed of CaCO3). Dolomite is also now known to precipitate directly from water in a few localities (e.g., some oceanic tidal flats and some lakes). Dolomite has a hardness of about 3.5 to 4 on the Mohs Hardness Scale. It tends to form pinkish or whitish curved rhombic crystals ("saddle dolomite"). Dolomite will bubble (effervesce) in acid if powdered first. The bubbles are carbon dioxide gas. If the acid is dilute hydrochloric acid, the chemical reaction is: 4HCl(aq) + CaMg(CO3)2(s) -->> 2CO2(g)↑ + 2H2O(l) + Ca+2(aq) + Mg+2(aq) + 4Cl-(aq) Pseudomorphs are minerals that have replaced other minerals, while retaining the crystal shape of the original mineral. Shown above is a halite crystal (NaCl - sodium chloride) that has been completely replaced by dolomite. Locality: undisclosed site north of Orion, western Major County, northwestern Oklahoma, USA Photo gallery of dolomite: www.mindat.org/gallery.php?min=1304 |
| Date | |
| Source | https://www.flickr.com/photos/47445767@N05/30438804405/ |
| 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@N05/30438804405. It was reviewed on 14 December 2020 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| current | 16:03, 14 December 2020 | | 1,790 × 1,784 (2.66 MB) | Ser Amantio di Nicolao (talk | contribs) | Uploaded a work by James St. John from https://www.flickr.com/photos/47445767@N05/30438804405/ with UploadWizard |
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