File:Manganoan calcite & quartz (Cretaceous; Huanggang Mine, Inner Mongolia, China) (43556234741).jpg
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| Description |
Manganoan calcite (= manganocalcite) from the Cretaceous of China. Pale pink = manganoan calcite Gray, glassy = quartz 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 carbonate minerals all contain one or more carbonate (CO3-2) anions. Calcite is a common mineral. It is calcium carbonate (CaCO3). It has a nonmetallic luster, commonly clearish to whitish to yellowish to grayish in color, is moderately soft (H≡3), moderately light-weight, has hexagonal crystals, and rhombohedral cleavage (three cleavage planes at 75º & 105º angles - cleavage pieces look like lopsided boxes). The easiest way to identify calcite is to drop acid on it - it easily bubbles (effervesces) in acid. The bubbles are carbon dioxide gas. If the acid is dilute hydrochloric acid, the chemical reaction is: 2HCl(aq) + CaCO3(s) -->> CO2(g)↑ + H2O(l) + CaCl2(aq) The most important & voluminous calcitic rocks in the world are limestone (sedimentary), marble (metamorphic), carbonatite (igneous), and travertine (speleothem, or "cave formations", and many hotspring deposits). Quite a few hydrothermal veins in the world are calcitic or have calcite as a principal component. The pale pink coloration present in the calcite shown above is from significant manganese impurity (Mn +2), resulting in the chemical formula (Ca,Mn)CO3. This sample comes from a skarn deposit in Inner Mongolia, which formed during the Cretaceous when granite intruded Lower Permian carbonate sedimentary rocks. Locality: Huanggang Mine, Inner Mongolia, northeastern China Photo gallery of manganoan calcite: <a href="https://www.mindat.org/gallery.php?min=2526" rel="nofollow">www.mindat.org/gallery.php?min=2526</a> Info. on locality: <a href="https://www.mindat.org/loc-64660.html" rel="nofollow">www.mindat.org/loc-64660.html</a> |
| Date | |
| Source | Manganoan calcite & quartz (Cretaceous; Huanggang Mine, Inner Mongolia, China) |
| 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@N05/43556234741 (archive). It was reviewed on 1 December 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| current | 09:08, 1 December 2019 | | 1,947 × 2,610 (2.72 MB) | Ser Amantio di Nicolao (talk | contribs) | Transferred from Flickr via #flickr2commons |
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