Hohmannite

from Wikipedia, the free encyclopedia
Hohmannite
Hohmannit mineralogical museum bonn.jpg
Hohmannite from Alcaparossa , Argentina
General and classification
other names

Castanite

chemical formula Fe 3+ 2 [O | (SO 4 ) 2 ] • 8H 2 O
Mineral class
(and possibly department) 		Sulfates (and relatives, see classification )
System no. to Strunz
and to Dana 		7.DB.30 ( 8th edition : VI / D.01)
09/31/04/01
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol triclinic pinacoidal; 1
Space group P 1 (No. 2)Template: room group / 2
Lattice parameters a  = 9.15  Å ; b  = 10.92 Å; c  = 7.18 Å,
α  = 90.3 °; β  = 90.8 °; γ  = 107.4 °
Formula units Z  = 2
Physical Properties
Mohs hardness 3
Density (g / cm 3 ) measured: 2.255; calculated: 2.250
Cleavage perfect according to {010}, imperfect according to {110} and {110}
colour orange, orange-brown to red-brown
Line color yellow-orange
transparency transparent to translucent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.559
n β  = 1.643
n γ  = 1.655
Birefringence δ = 0.096
Optical character biaxial negative
Axis angle 2V = 40 °
Pleochroism visible:
X = very light yellow
Y = light greenish yellow
Z = dark greenish yellow
Other properties
Chemical behavior disintegrates in hot water, dehydrated in air

Hohmannite is a very rare mineral from the mineral class of " sulfates (and relatives, see classification )". It crystallizes in the triclinic crystal system with the composition Fe 3+ 2 [O | (SO 4 ) 2 ] · (4 + 3) H 2 O, so it is chemically a water-containing iron sulfate.

Hohmannite is mostly found in the form of granular mineral aggregates , but rarely also forms short prismatic crystals up to about one millimeter in size and glass- shining surfaces. Its color varies between orange, orange-brown and red-brown, but its line color is yellow-orange .

Etymology and history

Hohmannite was first discovered in the area of Sierra Gorda in the Chilean Región de Antofagasta and described in 1887 by Friedrich August Frenzel , who named the mineral after the Chilean mining engineer and discoverer of the mineral Thomas Hohmann (1843-1897).

classification

In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , the Hohmannite belonged to the mineral class of "sulfates, chromates, molybdates, wolframates" and there to the department of "hydrous sulfates with foreign anions ", where it belongs together with amarantite , butlerite , Fibroferrit , Parabutlerit , Metahohmannit and Xitieshanit the "Butlerit-Amarantite group" with the system number. VI / D.01 .

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), assigns Hohmannite to the extended class of "sulfates (selenates, tellurates, chromates, molybdates and wolframates)" and there in the department of "Sulphates (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 octahedra and limited units ”, where it only forms the unnamed group 7.DB.30 together with amarantite and metahohmannite .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Hohmannite to the class of "sulfates, chromates and molybdates" and there to the category of "water-containing sulfates with hydroxyl or halogen ". Here he is to be found as the only member of the unnamed group September 31, 2004 within the sub-section “ Hydrogen sulfates with hydroxyl or halogen with (A + B 2+ ) (XO 4 ) Z q × x (H 2 O) ”.

Crystal structure

Hohmannite crystallizes triclinically in the space group P 1 (space group no. 2) with the lattice parameters a  = 9.15  Å ; b  = 10.92 Å; c  = 7.18 Å; α = 90.3 °; β = 90.8 ° and γ = 107.4 ° as well as 2 formula units per unit cell .

properties

In the air, Hohmannite dehydrates very quickly to Metahohmannite and it disintegrates in hot water.

Education and Locations

Amarantite (orange-red, needle-like) and Hohmannite (light orange, microcrystalline) on chalcanthite (blue) and copiapite (yellow) from the "Queténa Mine", Chuquicamata , Región de Antofagasta, Chile (size: 4.1 × 3.8 × 2, 5 cm)

Hohmannit formed as a low-temperature deposition in weathered iron sulfide - deposits . Amarantite, copiapite and metahohmannite, but also chalcanthite , cinnabarite , fibroferrite , picromerite , solid sulfur and sideron atrite are found as accompanying minerals .

As a very rare mineral formation, Hohmannite could so far (status: 2013) only be detected in a few samples from less than 10 sites. In addition to its type locality Sierra Gorda, the mineral appeared in Chile in two pits near Chuquicamata in the Región de Antofagasta and at Cerros Pintados in the Pampa del Tamarugal (Región de Tarapacá).

The only previously known site in Germany is a slate quarry near Lehesten in the Saalfeld-Rudolstadt district in Thuringia.

Hohmannite was also found in the "Santa Elena" mine near La Alcaparrosa in the Argentine province of San Juan , in the "Plaka" sulphate deposit near Lavrio (Ostattika) in Greece and in the "Redington Mine" near Knoxville in Napa County, California ( UNITED STATES).

See also

literature

Web links

Commons : Hohmannite  - 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 - Hohmannite
  3. ↑ a b c Hohmannite , in: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 66.6 kB )
  4. ↑ a b c d Mindat - Hohmannite
  5. ↑ Mindat - Number of localities for Hohmannite
  6. ↑ Mineral Atlas - Lehesten
  7. ^ Mineralienatlas - localities for Hohmannite