Amarantite

from Wikipedia, the free encyclopedia
Amarantite
Amarantite-Hohmannite-169933.jpg
Amarantite and Hohmannite from the Queténa Mine, Chuquicamata , El Loa Province, Región de Antofagasta, Chile
General and classification
chemical formula Fe 2 3+ [O | (SO 4 ) 2 ] • (3 + 4) H 2 O
Mineral class
(and possibly department) 		Sulfates (and relatives)
System no. to Strunz
and to Dana 		7.DB.30 ( 8th edition : VI / D.01)
09/31/03/01
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol triclinic pinacoidal; 1
Room group (no.) P 1 (No. 2)
Lattice parameters a  = 8.98  Å ; b  = 11.68 Å; c  = 6.70 Å,
α  = 95.6 °; β  = 90.4 °; γ  = 97.2 °
Formula units Z  = 2
Frequent crystal faces {100}, {010}
Physical Properties
Mohs hardness 2.5
Density (g / cm 3 ) measured: 2.189 to 2.286; calculated: 2.14
Cleavage completely according to {010} and {100}
Break ; Tenacity brittle
colour amaranth red to brownish or orange-red
Line color lemon yellow
transparency transparent
shine Glass gloss, matt
Crystal optics
Refractive indices n α  = 1.516
n β  = 1.598
n γ  = 1.621
Birefringence δ = 0.105
Optical character biaxial negative
Axis angle 2V = measured: 30 °; calculated: 52 °
Pleochroism visible: X = colorless; Y = light yellow; Z = reddish brown
Other properties
Chemical behavior well soluble in water

Amarantite is a rarely occurring mineral from the mineral class of "sulfates (and relatives)". It crystallizes in the triclinic crystal system with the chemical composition of Fe 2 3+ [O | (SO 4 ) 2 ] · (3 + 4) H 2 O and is therefore chemically seen a hydrous iron - sulfate with additional oxygen - ions .

Amarantite usually only develops small, prismatic crystals up to about 2 cm in length as well as needle-like, radial-rayed aggregates from amaranth- red to brownish-red or orange-red color with lemon-yellow streak color .

Etymology and history

Amarantite was first discovered in 1888 in the La Compañia mine near Caracoles in the province of Tocopilla , Región de Antofagasta in Chile and described in 1888 by Friedrich August Frenzel , who named the mineral after the Greek word αμάραντος for amaranth because of its characteristic color .

classification

In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the amarantite belonged to the mineral class of "sulfates, selenates, tellurates, chromates, molybdates, wolframates" and there to the department of "water-containing sulfates with foreign anions ", where it belongs together with butlerite the "butlerite-amarantite group" with the system no. VI / D.01 and the other members Fibroferrit , Hohmannit , Metahohmannit , Parabutlerit and Xitieshanit formed.

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 classifies amarantite in the category of "sulfates (selenates, etc.) with additional anions, with H 2 O". However, this is further subdivided according to the relative size of the cations involved and the crystal structure, so that the mineral is classified in the sub-section “With only medium-sized cations; isolated octahedron and limited units "can be found, where only together with Hohmannite and Metahohmannite the" Amarantite group "with the system no. 7.DB.30 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns amarantite to the class of "sulfates, chromates, molybdates" and there in the category of "water-containing sulfates with hydroxyl or halogen". Here he is the only member of the unnamed group 09/31/03 within the subdivision of " Water-containing sulfates with hydroxyl or halogen with (A + B 2+ ) (XO 4 ) Zq × x (H 2 O) ".

Crystal structure

Amarantite crystallizes triclinically in the space group P 1 with the lattice parameters a  = 8.98  Å ; b  = 11.68 Å; c  = 6.70 Å; α = 95.6 °; β = 90.4 ° and γ = 97.2 ° as well as 2 formula units per unit cell .

properties

Amarantite usually occurs in the form of broad, radial or finely needle-like to matted aggregates. The crystals, which are rarely well developed, are usually roughly square in cross-section and prismatically elongated along the c-axis, with the areas in the direction of the a- and b-axis dominating. Crystals which are tabular in the direction of the a-axis and crystal faces striped at right angles to the c-axis are also known. In total, more than 60 different crystal forms have been documented so far. Amarantite is readily soluble in water and weathers like ocher after a while .

Education and Locations

Amarantite is a secondary mineral that forms particularly under arid climatic conditions . Accompanying minerals include Hohmannite, Fibroferrit, Chalcanthite , Copiapit , Coquimbit and Sideronatrite .

So far (as of 2010) amarantite has been found at 20 sites worldwide. In Chile, in addition to its type locality La Compañia Mine, it came to light at several sites in the Región de Antofagasta as well as in Tierra Amarilla ( Región de Atacama ) and in the Pampa del Tamarugal .

Other locations include the Santa Elena Mine near La Alcaparrosa ( San Juan ) in Argentina; the Mutooroo Mine at Pine Creek, Northern Territory , Australia; Yazd in Iran; the Calamita Mine at Capoliveri in Italy; Otta in Norway; Dubník (Červenica) in Slovakia as well as near Blythe (California) , in San Juan County (New Mexico) and in the Broken Hill Mine (South Dakota) in the United States .

See also

literature

  • A. Frenzel: XVII. Mineralogical. 10. Hohmannite. 11. Amarantite. 12. Incidents in Ehrenfriedersdorf. In: Mineralogical and Petrographic Communications. Volume 9, 1888, pp. 397-400 ( PDF 192.8 kB )
  • P. Süsse: The crystal structure of amarantite, Fe 2 (SO 4 ) 2 O · 7H 2 O. In: Zeitschrift für Kristallographie. Volume 127, 1968, pp. 261–275 ( PDF 642.7 kB )
  • Paul Ramdohr , Hugo Strunz : Klockmann's textbook of mineralogy . 16th edition. Ferdinand Enke Verlag, 1978, ISBN 3-432-82986-8 , pp. 614, 839 .

Web links

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

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.  397 .
  2. ↑ Webmineral - Amarantite (English)
  3. ↑ a b c d Amarantite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 66.5 kB )
  4. ↑ a b c d Mindat - Amarantite (English)