File:Calcite (Magmont Mine, Iron County, Missouri, USA) 2.jpg

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English: Calcite crystals from Missouri, USA. (Dan & Diana Weinrich collection)

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 magnificent honey yellow-colored, scalenohedral calcite crystals shown above are from a zinc mine in the Viburnum Trend of southeastern Missouri. The Viburnum Trend is a roughly north-south trending zone of sulfide mineralization hosted in Upper Cambrian sedimentary rocks. The principal target minerals in the Viburnum Trend are galena and sphalerite, which are processed into lead and zinc. Numerous gangue minerals are also present, such as the calcite seen here. Mineralization in the Viburnum Trend is mostly in carbonate rocks of the Bonneterre Formation (Upper Cambrian). Orebody mapping has shown that mineralization occurred as basinal fluids traveled through the underlying Lamotte Sandstone (also Upper Cambrian) and rose up or around Precambrian basement highs that likely represented islands in a Late Cambrian sea. Mineralization probably occurred in the Late Paleozoic or Mesozoic.

Locality: Magmont Mine, Viburnum Trend Mining District, Southeast Missouri Lead District, southeast of the town of Bixby, far-western Iron County, southeastern Missouri, USA (vicinity of 37° 38' 22 North latitude, 91° 07' 21 West longitude)


Photo gallery of calcite: www.mindat.org/gallery.php?min=859


Some info. from:

Hagni (2006) - Directions of ore fluid flow in the Southeast Missouri Lead-Zinc District as inferred from asymmetrical distributions of orebodies around Precambrian knobs and from mineral/metal zoning patterns. Society for Mining, Metallurgy & Exploration Annual Meeting, March 27-March 29, 2006, St. Louis, Missouri Preprint 06-040. 15 pp.
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Source https://www.flickr.com/photos/47445767@N05/26816911495/
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@N05/26816911495. It was reviewed on 19 November 2020 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0.

19 November 2020

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