Asisit

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Asisit
Asisite - Kombat Mine, Namibia.jpg
Orange-colored asisite in Hausmannite from the Kombat Mine in Namibia
(image width 4 mm)
General and classification
other names

IMA 1987-003

chemical formula Pb 7 SiO 8 Cl 2
Mineral class
(and possibly department) 		Halides
System no. to Strunz
and to Dana 		3.DB.40 ( 8th edition : III / D.10)
02/10/07/01
Crystallographic Data
Crystal system tetragonal
Crystal class ; symbol ditetragonal-dipyramidal; 4 / m 2 / m 2 / m
Room group (no.) I 4 / mmm (No. 139)
Lattice parameters a  = 3.90  Å ; c  = 22.81 Å
Formula units Z  = 1
Physical Properties
Mohs hardness 3.5 to 4
Density (g / cm 3 ) calculated: 8.041
Cleavage completely after {001}
colour yellow to greenish yellow
Line color yellowish white
transparency transparent
shine Diamond luster
Crystal optics
Refractive indices n ω  = 2.390
n ε  = 2.320
Birefringence δ = 0.070
Optical character uniaxial negative

Asisite is a very rarely occurring mineral from the mineral class of " halides ". It crystallizes in the tetragonal crystal system with the chemical composition Pb 7 SiO 8 Cl 2 and has so far only been found in the form of transparent, tabular, approx. 0.5 mm crystals of yellow to yellow-green (occasionally also reddish-yellow) color with yellowish-white streak color .


Etymology and history

Asisit was first discovered in 1987 in the " Kombat Mine", which is located on the "Asis Farm" in the community of Grootfontein in Namibia.

The mineral was analyzed, scientifically described and named "Asis Farm" after its type locality by Roland C. Rouse , Donald R. Peacor , Pete J. Dunn , Alan J. Criddle , Chris J. Stanley and John Innes . It was recognized by the IMA as an independent mineral in the year of discovery under the internal accession number (IMA) 1987-003 .

classification

In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , it belonged to the mineral class of "halides" and there to the department of "oxyhalides", where together with blixite , chubutite , damaraite , ekdemite , heliophyllite , kombatite , mendipite , Mereheadit , Nadorit , Parkinsonit , Penfieldit , Perit , Philolithit , Pinalit , Sahlinit , Schwartzembergit , Seeligerit , Sundiusit , Symesit and Thorikosit an independent group formed.

The 9th edition of Strunz's mineral systematics , which has been valid since 2001 and is used by the International Mineralogical Association (IMA), also assigns the Asisit to the class of "halides" and there in the department of "oxyhalides, hydroxyhalides and related double halides" . This section is, however, further subdivided according to the type of cations involved , so that the mineral can be found according to its composition in the sub-section “With Pb, Cu etc.”, where it only includes the group named after these two minerals together with Parkinsonite the system no. 3.DB.40 forms.

The systematics of minerals according to Dana , which is common in the English-speaking world , assigns the Asisit to the class of "halides" and there in the department of "oxyhalides and hydroxyhalides". Here he is the only member of the unnamed group 02/10/07 within the subdivision " Oxihalides and hydroxyhalides with the formula A (O, OH) X q ".

Education and Locations

Asisite forms in manganese-containing silicate lenses near sulphide ore bodies. Accompanying minerals include barite , various chlorites , hematite , hematophanite , jacobsite , solid copper and molybdophyllite .

So far (status: 2010) the mineral could only be found at its type locality, the "Kombat Mine" in Namibia.

Crystal structure

Asisit crystallizes tetragonally in the space group I 4 / mmm (space group no. 139) with the lattice parameters a  = 3.90  Å and c  = 22.81 Å as well as one formula unit per unit cell .

See also

Individual evidence

  1. ↑ Webmineral - Asisite (English)
  2. ^ A b 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. 175 .
  3. ↑ a b c Asisite at mindat.org (engl.)
  4. ^ 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. 175 .

literature

  • 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. 175 .

Web links

Commons : Asisite  - collection of pictures, videos and audio files