Bishop

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Bishop
Bischofite - Antofagasta.JPG
Grainy bishofite from Antofagasta , Chile
General and classification
chemical formula MgCl 2  • 6H 2 O
Mineral class
(and possibly department) 		Halides
System no. to Strunz
and to Dana 		3.BB.15 ( 8th edition : III / A.12)
02/09/09/01
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic 2 / m
Room group (no.) C 2 / m (No. 12)
Lattice parameters a  = 9.86  Å ; b  = 7.11 Å; c  = 6.07 Å
β  = 93.8 °
Formula units Z  = 2
Twinning possibly polysynthetic twins under pressure
Physical Properties
Mohs hardness 1 to 2
Density (g / cm 3 ) measured: 1.591 to 1.604; calculated: 1.5895 (synthetic)
Cleavage no
Break ; Tenacity shell-like to uneven
colour colorless to white
Line color White
transparency translucent
shine Glass gloss to matt
Crystal optics
Refractive indices n α  = 1.495
n β  = 1.507
n γ  = 1.528
Birefringence δ = 0.033
Optical character biaxial positive
Axis angle 2V = measured: 79 °; calculated: 76 °
Other properties
Chemical behavior soluble in water
Special features astringent (astringent)

Bischofite is a rarely occurring mineral from the mineral class of " halides ". It crystallizes in the monoclinic crystal system with the composition MgCl 2  • 6H 2 O, so it is chemically a hydrous magnesium chloride .

Bischofite rarely develops colorless crystals with a short prismatic habit that are stretched along the c-axis. It is mostly found in the form of leafy, fibrous or granular mineral aggregates of white color, which only let the light shimmer through.

With a Mohs hardness of 1 to 2, bishofite is one of the soft minerals that, like the reference minerals talc (1) and gypsum (2), can be scratched with the fingernail.

Etymology and history

Bischofite was first discovered in the Leopoldshall potash works near Staßfurt and described by Carl Ochsenius (1830–1906), who named the mineral primarily after Karl Gustav Bischof (1792–1870), in recognition of his services to chemistry as one of the most important auxiliary sciences in geology to honor. At the same time, however, Ochsenius wanted the services of Bergrath and former director of the Staßfurt salt works F. Bischof to be recognized.

A mineral that Fischer initially described as bishopite in 1862 turned out to be the already known mineral plumbogummite after further investigations .

classification

In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , the bishofite belonged to the mineral class of the "halides" and there to the department of the "simple halides", where together with Antarcticit , Eriochalcite , Hydrohalite , Nickelbischofite , Rokühnit and Sinjarit one formed an independent 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), also assigns the bishofite to the class of “halides”, but there in the more finely subdivided division of “simple halides with H 2 O” " a. This department is further subdivided according to the molar ratio of the metal (M) involved to the halogen (X), so that the mineral can be found according to its composition in the subdivision "M: X = 1: 2", where it is the only member unnamed group forms 3.BB.15 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the bishop to the class and the division of the same name of "halides". Here he is the namesake of the "Bischofitgruppe" with the system no. 09.02.09 and the other member Nickelbischofit can be found within the subdivision of " Anhydrous and water-containing halides with the formula AX2 ".

Crystal structure

Bischofite crystallizes monoclinically in the space group C 2 / m (space group no. 12) with the lattice parameters a  = 9.86  Å ; b  = 7.11 Å; c  = 6.07 Å and β = 93.8 ° and 2 formula units per unit cell .

properties

Bischofite is easily soluble in water and very hygroscopic , so it quickly absorbs moisture from the environment and then dissolves . Therefore, the mineral should always be stored in an airtight container. In addition, Bischofite also has an astringent ( astringent ) effect .

Education and Locations

Bischofite is formed in saline deposits , but possibly also secondary from carnallite , with which it occurs in association with halite and kieserite .

As a rare mineral formation, bishofite could only be detected at a few sites so far (status: 2011). About 30 positions are known to date. In addition to its type locality Leopoldshall, the mineral also appeared in Germany in the pits “Berlepsch”, “Brefeld” ( Tarthun ) and near Aschersleben in Saxony-Anhalt as well as near Neuhof and in the Werra valley in Hesse; at Hänigsen , Wathlingen and Vienenburg in Lower Saxony and at Merkers in Thuringia.

Other locations include the "PCS Mine" near Rocanville in the Canadian province of Saskatchewan ; the Qinghai Lake , the Qarhan Salt Lake, and the Dalangtan Salt Lake in China; the “ Recsk Mine” in the Hungarian Mátra Mountains ; the mines "Santa Caterina" and "Pasquasia" in Sicily in Italy; in the Aksaital and near Atyrau in Kazakhstan; the Dutch municipality of Veendam ; Kłodawa in Poland; the Tolbachik volcano in the Kamchatka region of Russia ; Krasnoperekopsk in Ukraine ; and Carlsbad and the Tularosa Basin , Salduro, Utah, and Wendover in the United States.

See also

Individual evidence

  1. ↑ a b c d e 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. 157 .
  2. ↑ Webmineral - Bischofite (English)
  3. ↑ a b Handbook of Mineralogy - Bischofite (English, PDF 70 kB)
  4. ↑ a b c Bischofite at mindat.org (engl.)
  5. ↑ Mindat - Bischofite (of Fischer)
  6. ↑ Mindat - Number of localities for Bischofite

literature

Web links

Commons : Bischofite  - Collection of images, videos and audio files