Quadratit

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Quadratit
Quadratite.jpg
Quadratite crystals from the Lengenbach quarry, Binntal , Canton of Valais, Switzerland
General and classification
other names

IMA 1994-038

chemical formula Ag (Cd, Pb) [AsS 3 ]
Mineral class
(and possibly department) 		Sulfides and sulfosalts
System no. to Strunz
and to Dana 		2.GC.25 ( 8th edition : II / E.07)
04/03/11/03
Crystallographic Data
Crystal system tetragonal
Crystal class ; symbol ditetragonal-dipyramidal; 4 / m  2 / m  2 / m
Space group I 4 1 / amd (No. 141)Template: room group / 141
Lattice parameters a  = 5.50  Å ; c  = 33.91 Å
Formula units Z  = 8
Physical Properties
Mohs hardness 2.5 to 3
Density (g / cm 3 ) 5.31
Cleavage completely after {001}, clearly after {001}
colour black, dark gray, dark red
Line color reddish brown
transparency translucent to opaque
shine Metallic luster

Quadratite is a very seldom occurring mineral from the mineral class of sulfides and sulfosalts , more precisely a poly-sulfoarsenide with the chemical composition Ag (Cd, Pb) AsS 3 . It crystallizes in the tetragonal crystal system and has so far only been found in the form of microscopic (0.2 mm) to barely visible with the naked eye (1 to 2 mm), tabular crystals of black, dark gray or dark red color.

Etymology and history

The first samples of the new mineral were collected in 1989 in the “Lengenbach mine” in Binntal (Switzerland), but their investigation proved to be very difficult due to the tiny crystals of only 0.13 mm. At least it has already been proven that the unknown mineral is of tetragonal symmetry. Larger crystals of more than 1 mm were only found in 1993, which allowed a precise analysis and, above all, determination of all data necessary for recognition by the IMA / CNMNC .

A first scientific description followed in 1998 by Stefan Graeser , W. Lustenhouwer and P. Berlepsch, who named the mineral with reference to its characteristic square crystal shape, which was not found in any other Lengenbacher mineral.

classification

In the old systematics of minerals according to Strunz (8th edition) the quadratite still belongs to the undifferentiated division of the "sulfosalts" where it forms a separate group together with the crystal-chemically similar minerals Proustite , Pyrargyrite , Pyrostilpnite , Samsonite and Xanthocone .

With the restructuring in the 9th edition of Strunz's mineral systematics , the departments of the class of sulphides were partly redefined and divided more precisely. The mineral is now accordingly in the department of "sulfoarsenides, sulfoantimonides and sulfobismuthides" and there as the only one of its group in the subdivision of "poly-sulfarsenides".

The systematics of minerals according to Dana sorts the quadratite into the division of " sulfosalts with the ratio 3> z / y and the general composition (A + ) i (A 2+ ) j [ByCz], A = metals, B = semi-metals, C = non-metals "and there together with routhierite and stalderite in the unnamed subdivision" 03.04.11 ".

Crystal structure

Quadratite crystallizes tetragonally in the space group I 4 1 / amd (space group no. 141) with the lattice parameters a  = 5.50  Å and c  = 33.91 Å as well as 8 formula units per unit cell . Template: room group / 141

properties

morphology

The square shaped crystals get an octagonal shape by blunting the corners, whereby the longer edge mostly corresponds to the shape {100}. Under the microscope there is also often a square stripe arranged parallel {110}, which is evidence of the clear cleavage in this direction. Parallel to {001} the mineral shows a perfect, mica-like cleavage.

Education and Locations

So far, the mineral could only be detected at its type locality "Grube Lengenbach" and there exclusively in paragenesis with galena and jordanite , on which it was grown. In a larger yield from 1997, quadratites that grew directly on pyrite were also discovered .

See also

literature

  • Philippe Roth: Minerals First Discovered in Switzerland and Minerals Named After Swiss Individuals . Kristallografik Verlag, Achberg 2007, ISBN 3-9807561-8-1 , p. 124 . available online in Google Book Search

Web links

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

Individual evidence

  1. ↑ a b c d e 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.  126 (English).
  2. ↑ Webmineral - Quadratite (English)
  3. ↑ a b c Stefan Graeser, Ralph Cannon, Eva Drechsler, Thomas Raber, Philippe Roth: Faszination Lengenbach. Mining - Research - Minerals 1958 - 2008 . KristalloGrafik Verlag, ISBN 978-3-940814-16-6 , p. 110 Reading sample as PDF 1.2 MB; P. 14
  4. ↑ MinDat - Quadratite (English)