File:Dolomite after calcite, plus mottramite (Tsumeb Mine, Tsumeb, Namibia) 1.jpg
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DescriptionDolomite after calcite, plus mottramite (Tsumeb Mine, Tsumeb, Namibia) 1.jpg |
English: Dolomite pseudomorph after calcite, plus mottramite from Namibia.
Whitish = dolomite Greenish = mottramite 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 calcite mass (CaCO3 - calcium carbonate) that has been encrusted by dolomite. The original calcite has since dissolved away, leaving a hollow form. Such pseudomorphs are called "perimorphs". The green material is mottramite (PbCu(VO4)(OH) - lead copper hydroxy-vanadate). Locality: Tsumeb Mine, Tsumeb, southeastern Oshikoto Region, northern Namibia For information on the Tsumeb Mine, see: www.mindat.org/loc-2428.html |
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Source | https://www.flickr.com/photos/47445767@N05/30423092446/ |
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@N05/30423092446. 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. |
14 December 2020
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current | 16:03, 14 December 2020 | 2,572 × 1,960 (3.1 MB) | Ser Amantio di Nicolao (talk | contribs) | Uploaded a work by James St. John from https://www.flickr.com/photos/47445767@N05/30423092446/ with UploadWizard |
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Camera manufacturer | Canon |
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Camera model | Canon PowerShot D10 |
Exposure time | 1/15 sec (0.066666666666667) |
F-number | f/4.9 |
ISO speed rating | 80 |
Date and time of data generation | 13:35, 3 May 2014 |
Lens focal length | 18.6 mm |
Orientation | Normal |
Horizontal resolution | 180 dpi |
Vertical resolution | 180 dpi |
Software used | Adobe Photoshop CS2 Macintosh |
File change date and time | 21:49, 20 October 2016 |
Y and C positioning | Co-sited |
Exif version | 2.21 |
Date and time of digitizing | 13:35, 3 May 2014 |
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APEX shutter speed | 3.90625 |
APEX aperture | 4.59375 |
APEX exposure bias | −0.33333333333333 |
Maximum land aperture | 4.59375 APEX (f/4.91) |
Metering mode | Pattern |
Flash | Flash did not fire, compulsory flash suppression |
Supported Flashpix version | 1 |
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Focal plane resolution unit | inches |
Sensing method | One-chip color area sensor |
File source | Digital still camera |
Custom image processing | Normal process |
Exposure mode | Manual exposure |
White balance | Auto white balance |
Digital zoom ratio | 1 |
Scene capture type | Portrait |
Supported Flashpix version | 1 |
Image width | 2,572 px |
Image height | 1,960 px |
Date metadata was last modified | 17:49, 20 October 2016 |
IIM version | 2 |