Nahcolite

  • Thermokalit

Nahcolith is a rarely occurring mineral from the mineral class of " carbonates and nitrates " (formerly known as carbonates, nitrates and borates ). It crystallizes in the monoclinic crystal system with the composition of NaH [ CO3 ], and is therefore a chemical point of a sodium hydrogen carbonate.

Nahcolith rarely developed prismatic crystals. Usually in the form of porous mineral aggregates and efflorescence it occurs. In its pure form it is colorless and transparent. But it can also appear white and by foreign admixtures a gray, yellowish or reddish brown to black color accept, the transparency decreases according to the opacity. Through multiple light scattering due to lattice defects or polycrystalline training

With a Mohs hardness of 2.5 Nahcolith belongs to the soft minerals and is similar to the reference minerals gypsum and halite ( 2) and calcite (3) either still scratch with your fingernail or with a copper coin. The surfaces of undamaged crystals have a more glass-like shine on, cleavage planes, however greasy.

Special Features

Nahcolite is readily soluble in water and should be protected against humidity.

Etymology and history

Was first discovered Nahcolith at Vesuvius, ganauer in the " Atrio del Cavallo " (western part of the " Valle del Gigante " ) in Italy and described in 1928 by Frederick Allen Bannister ( 1901-1970 ), of the mineral according to its chemical composition (NaHCO ) and the Greek word for "stone" λίθος lithos named.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the Nahcolith belonged to the mineral class of " carbonates, nitrates and borates " and then to the Department of " water clear carbonate [ CO3 ] 2 - without foreign anions ", where he, together with Kalicinit the " Nahcolith - Kalicinit group " with the system no. Formed V/B.01 and the other members Natrit, Teschemacherit, Wegscheiderit and Zabuyelit.

The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the Nahcolith in the reduced class of " carbonates and nitrates ," there but also in the department of " Carbonates without additional anions, without H2O " one. However, this is further subdivided according to the affiliation of the cations involved at specific groups of elements, so that the mineral is found according to its composition in the subsection "Alkali - Carbonate ", where it forms the unnamed group 5.AA.15 the only member.

The mainly common in English-speaking classification of minerals according to Dana assigns a Nahcolith as the outdated Strunz'sche systematics in the common class of " carbonates, nitrates and borates " and there in the department of " carbonates ". Here he can be found as the only member of the unnamed group 13:01:01 within the subdivision " acid carbonates with different formulas ."

Education and Locations

Nahcolith forms as precipitation near heat sources, or as efflorescence in evaporation processes around salt lakes and alkalis. Also secondarily formed in the form of conversion edges on thermonatrite he may be found. Accompanying minerals occur in addition thermonatrite among other additional evaporite minerals such as borax, Burkeite Gaylussite, halite, Northupit, thenardite and trona.

A rare mineral formation Nahcolith could be detected only in a few localities, where so far (as of 2013) are considered to be known about 50 localities. Apart from its type locality " Atrio del Cavallo " at Vesuvius, the mineral in Italy could still be found at the Solfatara at Pozzuoli in Campi Flegrei.

Leading European localities include the Quarry " La Wiltz brook " near Bastogne in Belgium, the slag heaps of Ochsenhütte near Goslar ( Lower Saxony), the zinc smelter Genna at Letmathe (North Rhine -Westphalia ) and the copper-silver hut "God's reward" in Hettstedt (Saxony -Anhalt) in Germany, the Sokli - carbonatite complex near the community Savukoski in Finland, thermal springs near Abrest in France and around Karlovy Vary in the Czech Republic, Ditrau in Harghita County in Romania, Kukiswumtschorr and Alluaiw in the Chibinen on the Russian Kola Peninsula Alnön and Sandfors ( Västerbotten ) in Sweden and the salt mines at Bex in Switzerland.

Other localities lie in Egypt, Chile, China, Finland, Greenland, Canada, Kenya, Mexico, Mozambique, Namibia, Tajikistan, Tanzania, and in several states of the USA.

Crystal structure

Nahcolith crystallizes in the monoclinic space group P21 / c ( Raumgruppen-Nr. 14) with the lattice parameters a = 3.51 Å; b = 9.71 Å; c = 8.05 Å and 111.8 ° and β = 4 formula units per unit cell.

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