Chlorite group

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As chlorite (short chlorites from Greek. Chloros = green), a group of layer silicate - minerals from the mineral class of silicates and germanates referred, the general chemical composition (Fe, Mg, Al, Zn) 6 (Si, Al) 4 O 10 is (OH) 8 .

The elements in brackets can be mixed as desired, but are always in the same relationship to the elements listed in the other brackets of the formula. Chlorite has a relatively low hardness of 2 to 3, a green, sometimes yellow-brown color and a white streak color .

Chlorite: Cookeit

Etymology and history

The talc's magnesium-rich chlorite group was first scientifically described in 1862 by Alfred Des Cloizeaux and the mineral clinochlor by William Phipps Blake in 1851.

In special cases, chlorite minerals are rock-forming minerals. The first scientific description of the chlorite rocks comes from the year 1879 by Alexander Alexandrowitsch Inostranzew ( studies on the metamorphosed rocks in the Gouv. Olonetz ).

Single minerals and varieties

The Eisenendglied of chlorite is with Chamosite that Magnesiumendglied with Clinochlore that Manganendglied with Pennantit that Nick misery element with Nimit and Zinkendglied with Baileychlor referred.

Minerals of the group in detail:

Education and Locations

Chlorite occurs both massive and finely grained; also crystals occur, which are often combined in scaly aggregates. The mineral is found in igneous rocks , weakly metamorphosed rocks , the chlorite schist and chlorite rock as well as clayey sedimentary rocks . A well-known example is the Marx green marble from the Franconian Forest .

Furthermore, members of the chlorite group, in addition to kaolinite , are finely dispersed accompanying minerals from bauxite deposits . Sudoite and Donbasite occur in the French bauxite deposits of the Pyrenees , Gasconade County in the US state of Missouri and in some deposits in Hungary . Furthermore, other chlorite minerals such as clinochlor and chamosite can be found in other bauxite deposits.

structure

Chlorites are similar in structure and composition to mica . Similar to light and dark mica, they have tetrahedral layers made of SiO 4 and octahedron layers made of (Mg, Fe, Al) (OH) 6 , with a periodicity of TOT. There is an additional octahedron layer between the individual TOT groups, instead of an intermediate cation layer as in the "normal" mica. This means that Mg, Fe and Al (tri- vs. dioctahedral) can be incorporated in a further octahedral layer. If this octahedral layer consists of Mg (OH) 2 , it is also known as a brucite layer. Thus, the chemism of the chlorites varies from Al-poor (more trioctahedral phyllosilicates) to Al-rich chlorites (more dioctahedral phyllosilicates).

Use as a raw material

Chlorite vessel , found at Tepe Giyan, exhibited in the Louvre since 2003

Fragments of a suspected bangle made of polished chlorite, which were discovered in 2008 in the Denisova Cave in the Altai Mountains, famous for its Stone Age finds , have been indirectly dated to an age of around 40,000 years . It is the oldest known jewelry made from this material to date. Decorated chlorite vessels have been handed down from the third millennium BC . A center for this prehistoric production was Tepe Yahya in what is now Iran , where chlorite was found in abundance.

Chamosite and its particularly iron-rich variety thuringite occur as ooids in sedimentary rocks , associated with u. a. Magnetite , siderite and calcite . Such rocks are mined as iron ore .

See also

literature

  • Martin Okrusch, Siegfried Matthes: Mineralogy. An introduction to special mineralogy, petrology and geology . 7th edition. Springer Verlag, Berlin 2005, ISBN 3-540-23812-3 ( limited preview in the Google book search).
  • Hans Jürgen Rösler : Textbook of Mineralogy. 2nd revised edition. German publishing house for basic industry, Leipzig 1981.
  • Stefan Weiß: The large Lapis mineral directory. All minerals from A – Z and their properties. 4th edition, completely revised and supplemented. Christian Weise Verlag, Munich 2002, ISBN 3-921656-17-6 .

Web links

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

Individual evidence

  1. ↑ Rösler, 1981, p. 590.
  2. ^ FJ Loewinson-Lessing / EA Struve: Petrografitscheski Slowar . Moskwa 1937, p. 367.
  3. ^ György Bárdossy: The clay minerals of the bauxite deposits . In: R. Lauterbach (Ed.) Et al .: Clay minerals - genesis, deposits, industrial importance and use. Akademie-Verlag Berlin, Berlin 1976, pp. 11-12.
  4. ↑ Okrusch, Matthes, 2005, p. 104, limited preview in the Google book search.
  5. ↑ Anna Liesowska: Stone bracelet is oldest ever found in the world. The Siberian Times, May 7, 2015.