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Clusters of grunerite crystals from the Michigamme Mine, Marquette County, Michigan, USA (field of view 5 mm)
General and classification
chemical formula (Fe 2+ , Mg) 7 [OH | Si 4 O 11 ] 2
Mineral class
(and possibly department)
Chain silicates and band silicates (inosilicates)
System no. to Strunz
and to Dana
9.DE.05 ( 8th edition : VIII / F.07)
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group C 2 / m (No. 12)Template: room group / 12
Lattice parameters a  = 9.56  Å ; b  = 18.38 Å; c  = 5.34 Å
β  = 101.9 °
Formula units Z  = 2
Twinning simple to multiple twins in parallel {100}
Physical Properties
Mohs hardness 5 to 6
Density (g / cm 3 ) 3.4 to 3.6
Cleavage completely after {110}
Break ; Tenacity brittle
colour ash gray, brownish green, brown
Line color White
transparency translucent to opaque
shine Glass luster, pearlescent luster with a fibrous habit
Crystal optics
Refractive indices n α  = 1.663 to 1.686
n β  = 1.680 to 1.709
n γ  = 1.696 to 1.729
Birefringence δ = 0.033 to 0.043
Optical character biaxial negative
Axis angle 2V = measured: 90 to 70 °; calculated: 84 to 86 °
Pleochroism colorless, yellowish / greenish-yellow

The mineral grunerite even Grünerit , amosite , or brown asbestos called, is a rarely occurring chain silicate from the group of amphiboles . It crystallizes in the monoclinic crystal system with the chemical composition (Fe 2+ , Mg) 7 [OH | Si 4 O 11 ] 2 and develops mostly needle-like to fibrous, radial-ray crystals and aggregates of ash-gray or brownish-green to brown color. The crystals can be translucent and have a glass luster on their surfaces, with opaque, fibrous habit the surface shows a shimmering pearlescent luster.

Etymology and history

Grunerit was first discovered by the Swiss-French chemist Emmanuel Ludwig (Louis) Gruner (1809–1883) in the "Ravine de Sarvengude" near Collobrières in France, who also analyzed the mineral and described it in 1847. In 1853 Gustav Adolf Kenngott named the mineral after its discoverer.


Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the grunerite belonged to the mineral class of "silicates and germanates" and there to the department of "chain silicates and band silicates (inosilicates)", where together with cummingtonite ( magnesiocummingtonite ), Ferri-Klinoferroholmquistit , Klinoferroholmquistit , Manganocummingtonit , Manganogrunerit and Sodium-Ferri-Klinoferroholmquistit the subgroup of "Mg-Fe-Mn-Amphiboles" with the system no. VIII / F.07 within the amphibole 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 classifies Grunerit under the category of “chain silicates and band silicates (inosilicates)”. However, this is further subdivided according to the structure of the chains or bands as well as the allocation to related mineral families, so that the mineral according to its composition in the sub-section “Chain and band silicates with 2-periodic double chains, Si 4 O 11 ; Amphibole family, Klinoamphibole "is to be found, where it can be found together with anthophyllite, cummingtonite, ferri-clinoferroholmquistite, ferripedrite, ferro-anthophyllite, ferrogedrite, ferroholmquistite, ferropedrizit, fluorine-pedricite, gedrite, holmquistite, clinoferro-manganese gumquistite, manganese gumquistite Anthophyllite, sodium ferripedrite, sodium ferric ferropedrite, sodium ferrogedrite, sodium ferropedrite, sodium ferro anthophyllite, sodium drite, sodium pedricite, pedricite, permanganogrunerite, protoanthophyllite, protoferro anthophyllite and protomangano ferro-anthophyllite, the "protomangano-ferro-anthophyllite" , Mn-Klinoamphibole, Cummingtonitgruppe “with the system no. 9.DE.05 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the to the class of "silicates and germanates" and there in the department of "chain silicates: double unbranched chains, W = 2". Here he is in "Group 1, Mg-Fe-Mn-Li-Amphibole (Monoclinic)" with the system no. 66.01.01 can be found in the subsection “ Chain Silicates : Double unbranched chains, W = 2 amphibole configuration ”.

Crystal structure

Grunerite crystallizes monoclinically in the space group C 2 / m (space group no. 12) with the lattice parameters a  = 9.56  Å ; b  = 18.38 Å; c  = 5.34 Å and β = 101.9 ° and two formula units per unit cell . Template: room group / 12

Modifications and varieties

Fine-fiber, asbestos-like varieties of grunerite are known as amosite .

Education and Locations

Grunerite is formed by contact metamorphosis in medium to high grade iron formations and some blue schists . Accompanying minerals include fayalite , garnets , hematite , hedenbergite , magnetite , quartz and riebeckite .

So far (as of 2010) Grunerit has been found at around 150 sites worldwide, for example in Australia , Bolivia , Brazil , China , Finland , France , India , Japan , Cameroon , Canada , Madagascar , Norway , Austria , Portugal , Russia , Sweden , Slovakia , Spain , South Africa , the Czech Republic , Ukraine , Hungary , the United Kingdom (Great Britain) and the United States (USA).

Amosite is mainly mined in South Africa in the Asbestos Mines of South Africa . The term is an artificial word from the abbreviation of the South African mining company AMOS


As an asbestos-like material, amosite is no longer allowed to be used in Europe. In other countries, however, it is still partly used as building material.


In the event of prolonged exposure, there is a risk of serious damage to health through inhalation. The substance can cause cancer .

See also


Web links

Commons : Grunerite  - collection of images, videos and audio files

Individual evidence

  1. a b c d Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  626 (English).
  2. David Barthelmy: Grunerite Mineral Data. In: Retrieved on August 12, 2020 .
  3. Grunerite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( available online at [PDF; 79  kB ; accessed on May 10, 2018]).
  4. a b c d e Grunerite. In: Hudson Institute of Mineralogy, accessed August 12, 2020 .
  5. ^ Philippe Roth: Minerals first discovered in Switzerland and minerals named after Swiss individuals . 1st edition. Kristallografik Verlag, Achberg 2007, ISBN 3-9807561-8-1 , p. 182 .
  6. EL Gruner : Description d'un mineral nouveau dont la composition correspond à un pyroxène à base de fer (Note présentée par M. Dufreénoy) . In: Comptes rendus de l'Académie des sciences . tape  24 , 1847, pp. 794–795 ( available online at [accessed May 28, 2018]).
  7. ^ Gustav Adolf Kenngott: VIII. Order: Spathe. IX. Gender: Augit-Spathe. 4. Grunerit . In: The Mohs' mineral system . Publishing house and printing by Carl Gerold & Sohn, Vienna 1853, p. 62–77 ( available online at [PDF; 647 kB ; accessed on May 10, 2018]).