Dolomite (mineral)

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dolomite
Dolomite-Magnésite- Navarre.jpg
Dolomite (white) and magnesite from Eugui, Navarra, Spain
General and classification
other names

Dolomite spar

chemical formula CaMg [CO 3 ] 2
Mineral class
(and possibly department) 		anhydrous carbonates without foreign anions
System no. to Strunz
and to Dana 		5.AB.10 ( 8th edition : V / B.03)
02/14/01/01
Similar minerals Calcite , magnesite
Crystallographic Data
Crystal system trigonal
Crystal class ; symbol trigonal-rhombohedral; 3
Space group R 3 (No. 148)Template: room group / 148
Lattice parameters a  = 4.81  Å ; c  = 16.01 Å
Formula units Z  = 3
Frequent crystal faces Surfaces are often curved like a saddle
Twinning available
Physical Properties
Mohs hardness 3.5 to 4
Density (g / cm 3 ) measured: 2.86; calculated: 2.876
Cleavage completely after {10 1 1}; Segregation after {02 2 1}
Break ; Tenacity shell-like
colour colorless, white, yellow, brown
Line color White
transparency transparent to translucent
shine Glass gloss to pearlescent gloss
Crystal optics
Refractive indices n ω  = 1.679 to 1.681
n ε  = 1.500
Birefringence δ = 0.179 to 0.181
Optical character uniaxial negative
Pleochroism none
Other properties
Chemical behavior Dissolves very slowly in acid with formation of CO 2
Special features partially multicolored luminescence

Dolomite , also under the designations Dolomitspat , Rautenspat and Perlspat known, is a very common mineral in the mineral class of "carbonates and nitrates" with the chemical composition CaMg [CO 3 ] 2 and thus is chemically seen a Calcium - magnesium - carbonate .

Dolomite crystallizes in the trigonal crystal system and develops predominantly rhombohedral crystals or massive aggregates from white-gray to light brown in color. Its Mohs hardness is 3.5 to 4 and its density 2.9 g / cm³.

The dolomite rock of the same name consists of at least 90% the mineral dolomite.

Etymology and history

As an independent mineral , dolomite was discovered in 1792 by the Swiss mineralogist Horace-Bénédict de Saussure , who named it after the French geologist Déodat de Dolomieu . In the past, dolomite was also called bitter spar, but it does not taste bitter.

classification

In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , dolomite belonged to the mineral class of "carbonates, nitrates and borates " and there to the department of "anhydrous carbonates without foreign anions ", where it belongs together with anchorite , benstonite , ewaldite , Huntite , kutnohorite , minrecordite and norsethite formed the "dolomite group".

The 9th edition of Strunz's mineral systematics , which has been in force since 2001 and is used by the International Mineralogical Association (IMA), assigns dolomite to the class of “carbonates and nitrates” (the borates form a separate class here) and there to the “ Carbonates without additional anions; without H 2 O “. However, this section is further subdivided according to the type of cations involved , so that the mineral can be found according to its composition in the sub-section "alkaline earth (and other M 2+ ) carbonates", where it is only found together with ankerite, kutnohorite and minrecordite the "Dolomite Group" with the system no. 5.AB.10 forms.

The systematics of minerals according to Dana , like the outdated 8th edition of Strunz's systematics , assigns the dolomite to the common class of "carbonates, nitrates and borates" and there in the department of "anhydrous carbonates". Here it is together with anchorite, kutnohorite and minrecordite in the "dolomite group (Trigonal: R 3 )" with the system no. 01/14/01 to be found in the subsection of " Anhydrous carbonates with the formula A + B 2+ (CO 3 ) 2 ".

Crystal structure

Rhombohedron

Dolomite crystallizes in the trigonal crystal system in the space group R 3 (space group no. 148) with the lattice parameters a  = 4.8012  Å and c  = 16.002 Å as well as three formula units per unit cell . It crystallizes in the same crystal structure as calcite (homeotype). However, half of the calcium atoms have been replaced by the smaller magnesium atoms, which reduces the symmetry in the dolomite crystal accordingly. Template: room group / 148

properties

In comparison to other carbonates, dolomite is very difficult to attack by acids. The rate of reaction with acid is less than a thousandth that of calcite . The reason for this lies in the smaller ion size of the magnesium ion compared to the Ca ion, which means that the magnesium ion exchanges its ligands much more slowly; (in this case it is carbonate ions against water molecules). Only when the hydrochloric acid is warm does a reaction appear, in contrast to calcite, which reacts violently and noise with the hydrochloric acid.

If dolomite is dissolved in sulfuric acid , both gypsum and water-soluble magnesium sulfate (Epsom salt) are obtained in equivalent amounts . If you want to bring the reaction to an end in such a way that the solution no longer contains any acid, you must first pulverize the dolomite (or at least knock it into sand) and let the reaction with the acid take place in the heat.

The brittleness or lower plasticity can be explained mineralogically by the fact that the sliding surfaces in the geometrically similar crystal lattice of calcite are blocked by the different ion sizes of calcium (Ca) and magnesium (Mg).

Furthermore, the dolomite mineral exhibits a partially multicolored fluorescence in the colors orange to white, green and brown.

Modifications and varieties

The only known variety is cobalt dolomite , which has a pink color due to its cobalt content .

Education and Locations

Dolomite is formed by the interaction of magnesium-containing solutions with calcite sediments such as reef limestone. Sometimes it occurs alone in water that is particularly rich in magnesium or together with sulphide ores such as zinc blende or galena . He is one of the rock formers , the Italian Dolomites , for example, consist almost entirely of dolomite-rich sedimentary rock .

Most dolomite crystals come from the Gotthard , the burner and Greiner in the Tyrolean Alps and from Traversella in the Italian Piedmont .

Other sites include in Germany: Dietfurt (district of Treuchtlingen, Middle Franconia), Wachenzell (Upper Bavaria), Salzhemmendorf ( Ostfälisches Bergland), Nüxei (Harz / Southern Harz), Meskalith (Trier / Rhineland-Palatinate), mass limestone (Bergisches Land, Sauerland ); Hösbach-Rottenberg (Lower Franconia).

Worldwide: Brumado / Bahia in Brazil , Cavnic in Romania , Banská Štiavnica in Slovakia , Eugui in Spain and Jáchymov in the Czech Republic .

use

raw material

Dolomite rock is used as paving, brick, floor slabs, wall coverings, steps, design stones, armourstones, high-grade chippings for the concrete industry, building material, part of special cements , for steel production, for liming and as a raw material for the glass industry .

In water technology as a filter material and raw material for the production of Magno (chemical) , others also under dolomite (rock) and decarbonization .

The Chernobyl accident reactor was filled in with dolomite, among other things.

Gemstone

Colorless dolomite varieties are processed into gemstones in some cases . However, due to their physical properties (hardness, cleavage), they are very sensitive.

See also

literature

  • HB Saussure: Analysis de la dolomie . In: Observations sur la Physique, sur l'Histoire Naturelle et sur les Arts . tape 40 , 1792, pp. 161–173 ( rruff.info [PDF; 1,3 MB ; accessed on March 17, 2018]).
  • Petr Korbel, Milan Novák: Mineral Encyclopedia (=  Villager Nature ). Nebel Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 117 .
  • Hans Lüschen: The names of the stones. The mineral kingdom in the mirror of language . 2nd Edition. Ott Verlag, Thun 1979, ISBN 3-7225-6265-1 , p. 203 .

Web links

Commons : Dolomit (e)  - Collection of images, videos and audio files

Individual evidence

  1. ↑ a b c d Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  287 .
  2. ↑ a b c Dolomite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( handbookofmineralogy.org [PDF; 65  kB ; accessed on March 17, 2018]).
  3. ↑ a b c Mindat - Dolomite (English)
  4. ↑ List of localities for dolomite in the Mineralienatlas and Mindat