Bannisterite

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Bannisterite
Bannisterite-146436.jpg
2.5 x 1.7 cm group of black bannisterite crystals with brown bustamite from the North Mine, Broken Hill, Yancowinna County, New South Wales, Australia
General and classification
other names

IMA 1967-005

chemical formula (K, Ca) (Mn, Fe) 10 [(OH) 8 | (Si, Al) 16 O 38 ] • nH 2 O
Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		9.EG.40 ( 8th edition : VIII / H.17)
74.01.01.04
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic 2 / m
Room group (no.) A 2 / a (No. 15)
Lattice parameters a  = 22.32  Å ; b  = 16.4 Å; c  = 24.69 Å
β  = 94.3 °
Formula units Z  = 8
Physical Properties
Mohs hardness 4th
Density (g / cm 3 ) measured: 2.83 to 2.84; calculated: 2.84
Cleavage completely after {001}
colour light to dark brown, black
Line color light brown
transparency translucent
shine Resin gloss
Crystal optics
Refractive indices n α  = 1.544 to 1.574
n β  = 1.586 to 1.611
n γ  = 1.589 to 1.612
Birefringence δ = 0.045
Optical character biaxial negative
Axis angle 2V = calculated: 18 to 28 °

Bannisterite is a rarely occurring mineral from the mineral class of " silicates and germanates ". It crystallizes in the monoclinic crystal system with the chemical composition (K, Ca) (Mn, Fe) 10 [(OH) 8 | (Si, Al) 16 O 38 ] • nH 2 O and develops mostly prismatic to leafy crystals and mineral aggregates up to about 20 cm in size from light to dark brown and black in color with light brown streak color .


Etymology and history

Bannisterite was first discovered in 1936 in the "Benallt Mine" near Rhiw (Llanfaelrhys) on the Lleyn Peninsula in the United Kingdom (Great Britain) and described by Foshag, who, however, incorrectly identified the mineral as ganophyllite . When WC Smith compared the optical properties of the material known as ganophyllite from the “Benallt Mine” in 1948 with that of the same mineral from the type locality “Harstig Mine” near Pajsberg in Sweden , he was able to prove, due to the structural differences, that there are two minerals with the same Names had been assigned.

In 1968, ML Smith and C. Frondel were finally able to confirm the results of WC Smith with the help of X-ray diffraction diagrams on single crystals and named the material from the "Benallt Mine" bannisterite in honor of the curator of the mineral department of the British Museum in London.

Since material from the " Franklin Mine" in New Jersey (USA) was also used for the analysis of the mineral by ML Smith and C. Frondel, Franklin is also considered a type locality in addition to the "Benallt Mine" .

classification

In the meantime outdated, but still in use 8th edition of the mineral classification by Strunz of Bannisterit belonged to the mineral class of "silicates and Germanates" and then to the Department of " phyllosilicates (phyllosilicates)" where he collaborated with Bariumbannisterit , Eggletonit , Ekmanit , Franklinphilit , Ganophyllite , Lennilenapeit , Middendorfit , Parsettensit , Stilpnomelan and Tamait formed an independent group.

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 bannisterite to the class of “silicates and germanates” and there to the “phyllosilicates” section. This division is, however, further subdivided according to the type of stratification, so that the mineral can be found according to its structure in the sub-division "double nets with 6-membered rings", where together with Franklinphilit, Lennilenapeit, Parsettensit and Stilpnomelan it is the unnamed group 9. EG.40 forms.

The systematics of minerals according to Dana also assigns Bannisterite to the class of "silicates and germanates" and there in the department of "layered silicates: modulated layers". Here he is together with Stilpnomelan, Lennilenapeit, Franklinphilit and Middendorfit in the "Stilpnomelan group" with the system no. 74.01.01 to be found in the sub-section “ Layered Silicates: Modulated Layers with Connected Islands ”.

Education and Locations

Bannisterite and Rhodonite from Broken Hill , Yancowinna County, New South Wales, Australia

Bannisterite forms metamorphically in manganese and zinc-containing ore bodies . Accompanying minerals include amphiboles containing manganese and zinc , apophyllite , barite , calcite , fluorite , galena , quartz , rhodonite and sphalerite .

So far (as of 2011), Bannisterite has been detected at almost 20 sites around the world, including Broken Hill in Australia; several areas on Honshu and Shikoku in Japan; Botnedal in Tokke Municipality, Norway ; near Yekaterinburg in Russia; in the Slovak Ore Mountains ; in the Swedish community of Lindesberg (Västmanland) and near Sparta in Alleghany County of the US state of North Carolina.

Crystal structure

Bannisterite crystallizes monoclinically in the space group (space group no. 15) with the lattice parameters a  = 22.32  Å ; b  = 16.4 Å; c  = 24.69 Å and β = 94.3 ° and 8 formula units per unit cell .

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. 688 .
  2. ↑ Webmineral - Bannisterite (English)
  3. ↑ a b c d Bannisterite at mindat.org (engl.)
  4. ↑ a b c Peter J. Heaney, Jeffrey E. Post, Howard T. Evans, Jr .: The Crystal Structure of Bannisterite . In: Clays and Clay Minerals , Vol 40. No. 2. 129-144. 1992 (English, PDF 1.8 MB)

Web links

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