Alunogen

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Alunogen
Alunogen - Almyras, Agia Varvara, Cyprus.jpg
Alunogen from Almyras, Agia Varvara, Cyprus
General and classification
chemical formula Al 2 [SO 4 ] 3 • (12 + 5) H 2 O
Mineral class
(and possibly department) 		Water-containing sulfates without foreign anions
System no. to Strunz
and to Dana 		7.CB.45 ( 8th edition : VI / C.08)
08/29/06/01
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol triclinic-pinacoidal 1
Space group P 1
Lattice parameters a  = 7.42  Å ; b  = 26.97 Å; c  = 6.06 Å,
α  = 89.9 °; β  = 97.6 °; γ  = 91.9 °
Formula units Z  = 2
Twinning after {010}
Physical Properties
Mohs hardness 1.5 to 2
Density (g / cm 3 ) measured: 1.72 to 1.77; calculated: 1.79
Cleavage completely after {010}
Break ; Tenacity uneven
colour colorless, white, gray, yellowish, reddish
Line color White
transparency transparent
shine Glass gloss, silk gloss
Crystal optics
Refractive indices n α  = 1.473
n β  = 1.474
n γ  = 1.480
Birefringence δ = 0.007
Optical character biaxial positive
Axis angle 2V = 31 to 69 °
Other properties
Special features well soluble in water; bitter, astringent taste

Alunogen , sometimes out of date and synonymous also known as hair salt , ceramohalite , catharite or katherite , stipterite or stypterite or sulfuric acid alumina , is a rather seldom occurring mineral from the mineral class of sulfates . It crystallizes in the triclinic crystal system with the chemical composition Al 2 [SO 4 ] 3 • (12 + 5) H 2 O. It is therefore an aluminum sulfate containing water of crystallization (“hydrate”). Alunogen rarely develops transparent, tabular crystals or twins with pseudo-hexagonal symmetry a few millimeters in size. It is mostly found in the form of grape, kidney, stalactitic or fibrous to granular mineral aggregates and crusty coatings.

Etymology and history

The mineral was named after the Latin word "alum" for alum and the Greek word "genos" for source as an allusion to its use as a source of alum. Alunogen was first scientifically described in 1832 by François Sulpice Beudant .

classification

In the now outdated, 8th edition of the systematics of minerals according to Strunz , the alunogen belongs to the division of "water-containing sulfates without foreign anions ".

With the revision of Strunz's mineral system in the 9th edition , this section was subdivided more precisely according to the size of the cations involved and the alunogen can be found in the sub-section “With only medium-sized cations”.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , also sorts the alunogen into the class of sulfates (and related compounds), but there into the division of " hydrated acids and sulfates with the general composition (A) 2 (XO 4 ) 3  • x (H 2 O) “, where he is the only member of the unnamed group 08/29/06 .

Crystal structure

Alunogen crystallizes triclinically in the space group with the lattice parameters a  = 7.42  Å ; b  = 26.97 Å; c  = 6.06 Å; α = 89.9 °; β = 97.6 ° and γ = 91.9 ° as well as two formula units per unit cell .

properties

Pure Alunogen is colorless. However, due to its often fibrous to granular structure and the associated multiple refraction of light , it usually appears white . Different foreign admixtures Alunogen can also take on a gray, yellowish or reddish color.

Alunogen is easily soluble in water.

Education and Locations

Alunogen forms on the one hand as a weathering product in pyrite - and alumina-containing rocks , but on the other hand also by Resublimation arise from volcanic gases or burning heaps. Accordingly, alunogen is mostly found in paragenesis with pyrite and marcasite , but also with epsomite , gypsum , halotrichite , melanterite and pickeringite . Due to its high solubility in water, it happens sometimes that it in liquid form from coal - clefts swells.

Alunogen has so far (as of 2010) been detected at around 210 sites worldwide. Well-known locations for crystals include Adelaide in Australia , Friesdorf near Bonn in Germany , Opalbanya in Hungary , the Dexter No. 7 Mine at Calf Mesa , Utah and at Mt. Alum , New Mexico , USA . Alunogen can also be found in the form of aggregates in the Dubník opal mines in Slovakia .

See also

literature

Web links

Commons : Alunogen  - 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 Verlagsbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 384.
  2. ↑ Webmineral - Alunogen (English)
  3. ↑ a b c Alunogen at mindat.org (engl.)
  4. ↑ Mindat - Localities for Alunogen