Matildit

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Matildit
Matildite.jpg
Matildit from the Clara mine in Wolfach in the Black Forest , Baden-Wuerttemberg
General and classification
other names

Silver bismuth luster

chemical formula AgBiS 2
Mineral class
(and possibly department) 		Sulfosalts
System no. to Strunz
and to Dana 		2.CD.15 ( 8th edition : II / C.16)
07/03/01/01
Crystallographic Data
Crystal system trigonal
Crystal class ; symbol scalenohedral; 3 2 / m
Room group (no.) P 3 m 1 (No. 164)
Lattice parameters a  = 4.07  Å ; c  = 19.06 Å
Formula units Z  = 3
Physical Properties
Mohs hardness 2.5
Density (g / cm 3 ) 6.9
Cleavage Please complete!
Break ; Tenacity uneven
colour iron gray to black
Line color pale gray
transparency opaque
shine Metallic luster

Matildite is a rather seldom occurring mineral from the mineral class of " sulfides and sulfosalts ". It crystallizes in the hexagonal crystal system with the composition AgBiS 2 , so chemically speaking it is a silver - bismuth sulfide.

The rarely well-developed crystals are prismatic with an iron-gray, metallic sheen . Usually matildite occurs in coarse, granular masses or finely distributed in rock. Characteristic are tight adhesions with galena , which occasionally form textures similar to the Widmanstätten structure .

Etymology and history

Matildite was first discovered in the Matilda mine near Morococha in Peru and described in 1883 by Antonio D'Achiardi (1839–1902), who named the mineral after its type locality .

classification

Already in the now outdated, but still in use 8th edition of the mineral classification according to Strunz , Matildit belonged to the mineral class of "sulfides and sulfosalts" and there to the department of "sulfides with the molar ratio of metal: sulfur, selenium, tellurium = 1: 1", where together with aramayoite , tree strongite , bohdanowiczite , cuboargyite , miargyrite , schapbachite and volynskite, the unnamed group II / C.16 was formed.

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 assigns the matildite to the class of "sulfides and sulfosalts" and there in the department of "metal sulfides, M: S = 1: 1 (and similar) ”. This division is, however, further subdivided according to the predominant metals in the compound, so that the mineral, depending on its composition, can be found in the sub-division "with tin (Sn), lead (Pb), mercury (Hg) etc." where it can be found together with Bohdanowiczit and Volynskit the "Matildit group" with the system no. 2.CD.15 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the matildite to the class of "sulfides and sulfosalts" and there in the department of "sulfosalts". Here he is together with Bohdanowiczit, Volynskit and Zlatogorit in the "Matildit group" with the system no. 03.07.01 within the sub-section " Sulphosalts with the ratio z / y = 2 and the composition (A + ) i (A 2+ ) j [B y C z ], A = metals, B = semi-metals, C = non-metals " Find.

Modifications and varieties

Matildit (β-AgBiS 2 ) is the hexagonal low-temperature modification of the compound AgBiS 2 . At temperatures above 210 ° C, this changes to the cubic phase α-AgBiS 2 ( Schapbachite ). This structure is of the same type as that of PbS and both compounds form a complete series of mixtures at temperatures above 210 ° C. When it cools, such mixed crystals separate and form the typical oriented intergrowths of matildite and galena.

Lead contents of approx. 20 atom% of the cations stabilize the cubic structure even at low temperatures. Schapbachite was therefore later redefined and today denotes a ternary sulfosalt with a cubic PbS structure and the empirically determined composition Ag 0.80 Pb 0.35 Bi 0.81 S 2 or, more simply, Ag (Bi, Pb) S 2 .

Education and Locations

Matildite forms in hydrothermal deposits at high to medium temperatures and in pegmatites . The most microscopic crystals or earthy masses found grown in quartz or in aggregates with arsenides ( Cobaltit , Gersdorffit , Pararammelsbergit , rammelsbergite , safflorite , Skutterudit ), sulphides ( arsenopyrite , chalcopyrite , galena , Hessit , pyrite , sphalerite , tetradymite ) and Sulphosalts ( pavonite , aikinite , bismuthinite , tetrahedrite , stannite ) as well as solid bismuth and silver . Adhesions of matildite and bismuth have been described several times.

As a rather rare mineral formation, matildite can sometimes be abundant at various sites, but overall it is not very common. Around 170 sites are known to date (as of 2012). In addition to its type locality Mine Matilda (Morococha, Department Junín), the mineral also appeared in Peru in the Cerro de Pasco mine near Simón Bolívar in the Pasco region .

In Germany, Matildit was found in various locations in the Black Forest (Schapbach, Oberwolfach) in Baden-Württemberg; in the Bavarian Forest ( Silberberg near Bodenmais ), near Hagendorf ( Waidhaus ) and Wölsendorf ( Schwarzach near Nabburg ) in Bavaria and near Ehrenfriedersdorf (Sauberg, Schneeberg).

In Austria, the mineral was found mainly in Carinthia , more precisely at various sites in the Goldberg group and in the Pöllatal . In addition, it occurred in the Erzwies pit in the Gastein Valley and in several pits of the Rotgülden community in the Tamsweg (Lungau) district in Salzburg and at St Veit / Telfs in North Tyrol. In Switzerland, only the Formazzolo Alp sites in the Calnègia Valley (Ticino) and Gondo (Valais) are known to date .

Other locations are among others in Argentina, Australia, Bolivia, Bulgaria, Chile, China, France, Greece, Greenland, Iran, Italy, Japan, Canada, Mexico, Poland, Portugal, Norway, Romania, Russia, Sweden, Slovakia, Spain , South Korea, Tajikistan, Czech Republic, Tunisia, Turkey, Hungary, the United Kingdom (Great Britain) and the United States of America (USA).

Crystal structure

Matildit crystallizes trigonal in the space group P 3 m 1 (space group no.164) with the lattice parameters a  = 4.07  Å and c  = 19.06 Å as well as 3 formula units per unit cell .

The structure of matildite, like that of galena and schapbachite, can be derived from the sodium chloride structure. Each sulfur ion is surrounded by six cations and each cation (Ag, Bi) by six sulfur anions. The sulfur atoms mark the corners of a slightly distorted octahedron, in the center of which the cation is located (octahedral coordination).

The AgS 6 octahedra are connected to one another via common edges to form layers. The same applies to the BiS 6 octahedra. These layers are stacked alternately on top of one another in the direction of the crystallographic c-axis. Here, the AgS 6 octahedra of one layer are linked to the BiS 6 octahedra of the surrounding layers via common edges .

See also

literature

Web links

Individual evidence

  1. ↑ John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols: Matildit , in: Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 62.5 kB )
  2. ↑ a b c d 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.  91 .
  3. ^ Albert Huntington Chester: A dictionary of the names of minerals including their history and etymology , New York, J. Wiley & sons; London 1896, p. 169 ( available online at Internet Archive )
  4. ^ The Mineralogical Record - D'Achiardi, Antonio
  5. ↑ Kurt Walenta, Heinz-Jürgen Bernhardt, Thomas Theye: Cubic AgBiS 2 (schapbachite) from the Silberbrünnle mine near Gengenbach in the Central Black Forest, Germany , in: Neues Jahrbuch für Mineralogie - Monatshefte (2004), Volume 9, p. 425 -432 doi : 10.1127 / 0028-3649 / 2004 / 2004-0425
  6. ↑ Mindat - Number of locations for Matildit (English)
  7. ^ Mindat - Matildite