File:Calcite (Stillwater Mine, Beartooth Mountains, Montana, USA) 1.jpg

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English: 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 5600 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). Many hydrothermal veins in the world are calcitic or have calcite as a principal component.

The honey yellow calcite crystals seen here are from an underground mine in Montana - the famous Stillwater Mine, which produces platinum and palladium. The platinum ores are very old, Precambrian rocks. The calcite is late-stage, fracture-lining mineralization unrelated to the formation of those rocks.

Geologic context: crystal-lined, open fracture in rocks of the Johns-Manville Reef, Troctolite-Anorthosite I zone, Lower Banded Series, Stillwater Complex, upper Neoarchean, 2.7 Ga

Locality: Stillwater Mine, southwest of the town of Nye, southwestern Stillwater County, Beartooth Mountains, southern Montana, USA


Photo gallery of calcite:

www.mindat.org/gallery.php?min=859
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Source https://www.flickr.com/photos/47445767@N05/50820337987/
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@N05/50820337987. It was reviewed on 11 January 2021 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0.

11 January 2021

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current14:40, 11 January 2021Thumbnail for version as of 14:40, 11 January 20212,351 × 1,931 (2.99 MB)Ser Amantio di Nicolao (talk | contribs)Uploaded a work by James St. John from https://www.flickr.com/photos/47445767@N05/50820337987/ with UploadWizard

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