Calcite

The calcite is a Minéral chemical or biochemical (biomineralisation) composed of natural carbonate of calcium (CaCO3), Cristal reading in the principal system rhomboedric and constituting many sedimentary rocks: Calcareous S, marl S; it is one of the most abundant carbonates.

The calcite-colloid is a variety of colloidal calcite.

Color: pure calcite is white. The presence of cations other than calcium, and in particular of metals of transition, gives him a coloring allochromatic yellow, orange, red, green, blue, brown, gray.

Luminescence: Mn2+ activates while Fe2+ removes the Cathodoluminescence calcite.

Discusses on classification

Although calcite is classically described like rhomboedric, Massimo Nespolo, professor of mineralogy, affirm that it is more precisely trigonal with network rhomboedric (see the article on the crystalline structure for the complete explanation of the problem).

Properties

Calcite crystallizes in the trigonal system and an infinite crystal pallet. The unit of the network is an acute rhombohedron, containing two molecules of CaCO3 whose characteristics are:
  • length of the edge: 6,36. 10-10 m
  • angle enters the axes: 46°6',
  • distance between 2 plans identical & parallel with the face of cleavage: 3,03. 10-10 m
  • volume of a molecule of the crystal: 60,75. 10-30 m ³
Calcite is pure and colorless blanchâtre. Its Density is of 2,71 kg/dm ³. It is classified of hardness 3 in the scale of hardness of Mohs. Its Solubilité in pure water is about 15 to 20 Mg per liter. Its Specific heat is about 81,80 J·mol-1·K-1 (19,57 cal/mol.°C) with 25°C.

Calcite, in its forms resulting from the mining (Calcareous, Carbonate of calcium) has very great industrial applications: in the construction industry (cement, lime, stones of ornament,…), like flux in the glassmaking & the metallurgy; it provides raw materials for chemical industry, the manufacture of manure and much of other uses.

Crystallized calcite is sometimes called Iceland spar , whose most beautiful crystals were used in the polarization of the light.

Optical properties

Calcite is a mineral with cleavage Net. It colorless or is slightly coloured brown in not analyzed polarized light (or light known as " natural ") with irisations on the level of cleavages. It has a Pléochroïsme very marked relief. In analyzed polarized light , calcite polarizes in the colors pastel of order three, mainly in colors pink and green.

See too

  • a transition from phase “geographical”: the strange case of quartz.
  • File on calcite and limestone: Calcite

  • Schmittner Karl-Erich and Giresse Pierre, 1999. Microphone-environmental controls one biomineralization: superficial processes off apatite and calcite precipitation in Quaternary soils, Roussillon, France. Sedimentology 46/3: 463-476.

Simple: Calcite

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