Allactite

from Wikipedia, the free encyclopedia
Allactite
Allactite-116056.jpg
Pale pink allactite from the type locality Moss Mine, Nordmark (Nordmarksberg), Filipstad , Värmland, Sweden (image size: 3 mm)
General and classification
other names
  • Chloroarsenian
  • Elfstorpit
chemical formula Mn 2+ 7 [(OH) 4 | AsO 4 ] 2
Mineral class
(and possibly department) 		Phosphates, arsenates and vanadates
System no. to Strunz
and to Dana 		8.BE.30 ( 8th edition : VII / B.15)
02.41.01.01
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group P 2 1 / a (No. 14, position 3)Template: room group / 14.3
Lattice parameters a  = 11.03  Å ; b  = 12.12 Å; c  = 5.51 Å
β  = 114.1 °
Formula units Z  = 2
Physical Properties
Mohs hardness 4.5
Density (g / cm 3 ) measured: 3.83; calculated: 3.94
Cleavage clearly after {001}
Break ; Tenacity uneven; brittle
colour brown to brownish red, dark to light red violet, colorless to white
Line color gray to pale brown
transparency translucent
shine Glass gloss, weak greasy gloss on cleavage surfaces
Crystal optics
Refractive indices n α  = 1.755 to 1.761
n β  = 1.772 to 1.786
n γ  = 1.774 to 1.787
Birefringence δ = 0.019 to 0.026
Optical character biaxial negative
Axis angle 2V = 36 ° (calculated)
Pleochroism Visible: X = blood red; Y = light yellow; Z = sea green

Allactite is a very rare mineral from the mineral class of "phosphates, arsenates and vanadates". It crystallizes in the monoclinic crystal system with the chemical composition of Mn 2+ 7 [(OH) 4 | AsO 4 ] 2 and thus is chemically seen a manganese - arsenate with additional hydroxide .

Allactite develops narrow, tabular to prismatic crystals up to about six millimeters in length and a glass-like sheen on the surfaces. The color of the mineral varies depending on the foreign admixtures from brown to brownish red or dark to light red violet. Allactite crystals that are almost colorless to white can also be found very rarely. The streak color , on the other hand, is gray to pale brown.

Allactite is the arsenate analogue of argandite (Mn 7 [(OH) 4 | VO 4 ] 2 ) discovered in 2010 .

Etymology and history

Allactite was first discovered in the Moss Mine on Nordmarksberg near Nordmark ( Filipstad municipality ) in the Swedish province of Värmland and described in 1884 by Hjalmar Sjögren , who named the mineral after the pseudo- ancient Greek word αλλάκτειν [alláktein] (correctly ἀλλάσσειν [allássein] * ἀλλαg- * allag-) for change or change named. Sjögren chose the name because of the strong pleochroism , i.e. the clearly visible color change when looking at the mineral from different perspectives.

In 1893, Lars Johan Igelström (1822-1897) described a newly discovered mineral from the Sjögruvan (see also Rällingsberg mine ) near Grythyttan ( Hällefors municipality ) in the Swedish province of Västmanland under the name Elfstorpit (after the local company Elfvestorp Eisenwerke). Only around a hundred years later did F. Fontan, D. Holtstam, P. de Parseval, F. Permingeat and B. Mason prove in their publication from 2004 by means of a powder X-ray diffraction analysis on the type material and other specimens of Elfstorpit that the material was not differed from allactite. The mineral name Elfstorpite was then discredited and has been a synonym for Allactite ever since.

classification

Allactite belonged to the mineral class of "phosphates, arsenates and vanadates" and there to the department of "anhydrous phosphates, with foreign anions F, Cl, O, OH", in the outdated, but partly still in use, 8th edition of the mineral classification according to Strunz . where he together with Flinkit , Raadeit , Retzian- (Ce) , Retzian- (La) , Retzian- (Nd) and Waterhouseit formed the unnamed group VII / B.15 .

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 the allactite to the category of “phosphates etc. with additional anions; without H 2 O “. However, this is further subdivided according to the relative size of the cations involved and the molar ratio of the additional anions to the phosphate, arsenate or vanadate complex, so that the mineral is classified in the sub-section “With only medium-sized cations; (OH etc.): RO 4  > 2: 1 "can be found, where together with Flinkit the" Flinkit-Allaktit-Gruppe "with the system no. 8.BE.30 and the other member Raadeit.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the allactite to the class of "phosphates, arsenates and vanadates" and there to the category of "anhydrous phosphates etc., with hydroxyl or halogen". Here he is the sole namesake of the " Allaktitgruppe " with the system no. 41.02.01 and the other members Raadeit and Waterhouseit can be found in the subsection "Anhydrous phosphates etc., with hydroxyl or halogen with (AB) Z 7 (XO 4 ) 2 Z q ".

Crystal structure

Allactite crystallizes monoclinically in the space group P 2 1 / a (space group no. 14, position 3) with the lattice parameters a  = 11.03  Å ; b  = 12.12 Å; c  = 5.51 Å and β = 114.1 ° and two formula units per unit cell . Template: room group / 14.3

properties

As the name of the mineral suggests, Allactite has pronounced pleochroistic properties and shows a different color depending on the direction from which the light passes through the crystal. The mineral therefore appears blood red in the direction of the x-axis, light yellow in the direction of the y-axis and sea-green in the direction of the z-axis.

Education and Locations

Reddish allactite crystals on solid lead from Långban, Sweden (size: 4 cm × 2.6 cm × 1.2 cm)
Brownish red allactite aggregate from the Sterling Mine, Sterling Hill, Sussex County (New Jersey), USA (field of view 3.7 mm × 2.5 mm)

Allactite forms as a secondary mineral in small veins that run through metamorphically altered manganese deposits . It can also converted into metamorphic, layered (stratiform) zinc - ore bodies occur. Due to its formation conditions can allactite with many different minerals associated to be like among other adelite , barite , calcite , fluorite , Franklinite , Friedelite , Hämatolith , Hausmannite , Hodgkinsonit , Karyopilit , Leukophönicit , Pyroaurit , Pyrochroit , sphalerite , Synadelphit , Willemit and various chlorites and serpentine .

As a rare mineral formation, allactite could only be detected at a few sites, whereby so far (as of 2015) around 10 sites are known. In addition to its type locality Moss Mine, the mineral was also found in Sweden in the Brattfors, Finngruvan-Gröngruvan and Kittel pits, which are also nearby in Nordmark, as well as at Långban and the Harstigen mine near Pajsberg in the Filipstad municipality in Värmland.

Other well-known locations for allactite are the "Iron Monarch" open pit mine near Iron Knob on the Eyre Peninsula in South Australia as well as the Franklin Mine in the well-known mining district of Franklin (New Jersey) and the Sterling Mine near Sterling Hill (Ogdensburg municipality) in Sussex County (New Jersey) in the United States of America.

See also

literature

Web links

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

Individual evidence

  1. ↑ International Mineralogical Association : International Mineralogical Association: Commission on new minerals and mineral names. In: Mineralogical Magazine Volume 43 (1980), pp. 1053-1055 ( PDF 171.9 kB ).
  2. ↑ a b LJ Igelström: Mineralogiska meddelanden. 20. Nya mineral från Sjögrufvan. In: Geologiska Föeningens i Stockholm. Conveyor handler. Volume 15 (1893), pp. 471-472.
  3. ↑ 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.  449 .
  4. ↑ a b c d Allactite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 63.7 kB ) .
  5. ↑ a b c d e f Mindat - Allactite .
  6. ↑ Olle Franzén: Lars Johan Igelström at sok.riksarkivet.se.
  7. ↑ Elfstorpite In: A dictionary of the names of minerals inluding their history and etymology Cornell University Library , 1891, p. 83 ( available online at archive.org ).
  8. ↑ F. Fontan, D. Holtstam, P. de Parseval, F. Permingeat, B. Mason: Elfstorpite synonymy with allactite; mineral and name discredited. In: Mineralogical Magazine. Volume 68, No. 3 (2004), pp. 523-526 doi : 10.1180 / 0026461046830203
  9. ↑ Mindat - Elfstorpite .
  10. ↑ Mindat - Number of localities for allactite .
  11. ↑ Find location list for allactite in the Mineralienatlas and Mindat