Dolomite

• Dolomitspat

Dolomite, also known under the names Dolomitspat, Rautenspat and Perlspat is a very common mineral from the mineral class of anhydrous carbonates without foreign anions. It crystallizes in the trigonal crystal system with the chemical composition CaMg [ CO3 ] 2 and developed predominantly rhombohedral crystals or massive aggregates of whitish-gray to light brown color. Its Mohs hardness of 3.5 to 4, and its density is 2.9 g / cm ³.

The same dolomite comprises at least 90 % of the mineral dolomite.

Properties

Dolomite is very difficult to attack compared to other carbonates by acids. The rate of reaction with acid is at least 1000 times slower than that of calcite. The reason for this is the smaller size of the magnesium ion - ion in relation to the Ca - ion, which results in that the magnesium its ligand exchange more slowly; (in this case, there are carbonate ions for water molecules). Only with warm hydrochloric acid shows a reaction, in contrast to calcite, which reacts violently and noise with the hydrochloric acid.

Solving dolomite in sulfuric acid, is obtained in equivalent amounts of both gypsum and the water-soluble magnesium sulfate ( Epsom salt). If we would like to bring the reaction to the end that the solution at the end contains no acid, you must first dolomite powder (or at least sand zerklopfen ) and the reaction with the acid in the heat can take place.

The brittleness or plasticity less likely mineralogical thus be explained that existing at geometrically similar design crystal lattice of calcite sliding surfaces by the different ionic size of calcium (Ca ) and magnesium (Mg ) are blocked.

Furthermore, the mineral dolomite, a partial multi-colored fluorescence in shades of orange to white, green and brown on.

Etymology and history

Was recognized as an independent mineral dolomite in the late 18th century by the Swiss mineralogist HB de Saussure, who named it after the French geologist Déodat de Dolomieu. Previously dolomite also had the name Bitterspat, but it does not taste bitter.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the dolomite belonged to the mineral class of " carbonates, nitrates and borates " and then to the Department of " water clear carbonates without foreign anions ", where he along with ankerite, Benstonit, Ewaldit, huntite, Kutnohorit, Minrecordit and Norsethit the " dolomite group " was formed.

The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the dolomite in the class of " carbonates and nitrates " ( here, the borates form a separate class) and then in the Department of " carbonates without further anions, without H2O ". This division, however, is further subdivided according to the nature of the cations involved, so that the mineral is found according to its composition in the subsection " alkaline-earth (and other M2 ) carbonates " where there is only together with ankerite, Kutnohorit and Minrecordit the " dolomite group "with the system no. 5.AB.10 forms.

The classification of minerals according to Dana assigns the dolomite as the outdated 8th edition of the Strunz'schen systematics in the common class of " carbonates, nitrates and borates " and there in the department of " water clear carbonates ". Here he is with ankerite, Kutnohorit and Minrecordit in the " dolomite group ( Trigonal: R3) " with the system no. 14:01:01 within the sub-division of " water clear 2 carbonates having the formula A B2 ( CO3) " to find.

Varieties

As a single variety of the cobalt dolomite is known by its cobalt content has a pink color.

Education and Locations

Dolomite formed by interaction of magnesium-bearing solutions with calcite sediments as Riffkalkstein. Sometimes it also occurs alone in particularly magnesium-rich water or with sulphide ores such as sphalerite or galena. He belongs to the rock -forming agents, the Italian Dolomites for example be almost entirely of dolomite -rich sedimentary rocks.

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

Other localities include in Germany: Unterdietfurt (OT v. Treuchtlingen, Middle Franconia ), guard cell (Upper Bavaria), Salzhemmendorf ( Ostfälisches Bergland ), Nüxei ( resin / South Harz ), Meskalith (Trier / Rhineland -Palatinate ), Massenkalk ( Bergisch Land, Sauerland); Hösbach - Rottenberg ( Lower Franconia ).

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

Crystal structure

Dolomite crystallizes in the trigonal crystal system in the space group R3 ( trigonal- rhombohedral ) with the lattice parameters a = 4.8012 Å and c = 16.002 Å and three formula units per unit cell. It crystallizes in the same crystal structure, such as calcite ( homöotyp ). However, half of the calcium atoms is replaced by the smaller magnesium atoms, which lowers the symmetry in the dolomite crystal accordingly.

Use

Commodity

Applies dolomite as plaster, brick, floor tiles, wall cover, steps, shaping stones, water blocks, chippings for the concrete industry, building material, part of special cements, for steel production and as raw material for the glass industry.

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

The disaster - Chernobyl reactor was filled with dolomite, among others.

Gem

Colorless dolomite varieties are processed in some cases, semi-precious stones. However, they are very sensitive by their physical properties (hardness, cleavage ).