Douglasite

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Douglasite
General and classification
other names

Iron chlorochloride potassium

chemical formula K 2 [Fe 2+ Cl 4 (H 2 O) 2 ]
Mineral class
(and possibly department) 		Halides
System no. to Strunz
and to Dana 		3.CJ.20 ( 8th edition : III / C.07)
03/11/01/01
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol 2 / m
Lattice parameters a  = 11.80  Å ; b  = 16.27 Å; c  = 8.22 Å
β  = 104.9 °
Formula units Z  = 6
Physical Properties
Mohs hardness nd
Density (g / cm 3 ) measured: 2.16; calculated: [2.04]
Cleavage indistinct
colour light green, yellow green, brownish red
Line color Please complete!
transparency translucent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.488
n β  = 1.488
n γ  = 1.500
Birefringence δ = 0.012
Optical character uniaxial positive
Axis angle 2V = 5 °

Douglasite is a very rarely occurring mineral from the mineral class of " halides ". It crystallizes in the monoclinic crystal system with the composition K 2 [Fe 2+ Cl 4 (H 2 O) 2 ], so it is chemically a water-containing potassium - iron - chloride .

Douglasite could only be found in the form of coarse-grained masses of translucent light green, yellow-green or brownish-red color.

Etymology and history

Douglasite was first discovered in the salt clay near Douglashall a few kilometers west of Westeregeln on the northwestern edge of the Salzlandkreis in Saxony-Anhalt . It was described in 1880 by Heinrich Precht (1852-1924), who received the mineral from Carl Ochsenius and named it after its type locality at his suggestion .

Type material of the mineral can be found in "The Natural History Museum" in London (England) under the register no. 1965,450 .

classification

Now outdated already in, but still in use 8th edition of the mineral classification by Strunz was one of Douglasit the mineral class of "halides" and then to the Department of "Doppelhalogenide, hydrated," where he along with Erythrosiderit , Kremersit and Mitscherlichit the independent group III / C.07 formed.

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also assigns Douglasite to the “halides” class and there to the “complex halides” department. However, this section is further subdivided according to the crystal structure and partly according to the predominant metals in the compound, so that the mineral is classified in the sub-section “With MX 6 complexes; M = Fe, Mn, Cu ”is to be found, where it is the only member of the unnamed group 3.CJ.20 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Douglasite to the “halides” class and there to the “complex halides - aluminum fluorides” division. Here he is to be found as the only member of the unnamed group 11.03.01 within the subdivision of the " Complex halides - aluminum fluorides with (A) m B (X) 4 • x (H 2 O) ".

Crystal structure

Douglasite crystallizes monoclinically with the lattice parameters a  = 11.80  Å ; b  = 16.27 Å; c  = 8.22 Å and β = 104.9 ° and 6 formula units per unit cell . The exact space group has not yet been determined.

Education and Locations

Douglasit formed by sedimentation or evaporation including in potash - deposits . Accompanying minerals include carnallite , sylvin and halite .

So far (status: 2011) Douglasite could only be detected at its type locality Douglashall in the Staßfurt potash deposit .

See also

literature

  • Boeke: New Yearbook for Mineralogy, Geology and Paleontology. Heidelberg / Stuttgart 1909, II, p. 44.
  • ES Larsen: The Microscopic Determination of the Nonopaque Minerals. 1st edition. USGS Bulletin 679, 1921, p. 69.
  • Carl Ochsenius : The formation of rock salt deposits and their mother liquor salts with special consideration of the Douglashall flotch in the Egeln'schen Mulde. Publishing house CEM Pfeffer, Halle 1877.

Web link

Individual evidence

  1. ↑ a b H. Precht : About the formation of hydrogen in the Stassfurt Precht potash mines. Reports of the German Chemical Society. Berlin 13, pp. 2326–2328 ( PDF 352.2 kB )
  2. ↑ a b c d Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  169 .
  3. ^ A b c John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols: Douglasit. In: Handbook of Mineralogy, Mineralogical Society of America. 2001 ( PDF 68.4 kB )
  4. ↑ a b c d MinDat - Douglasite (English)