Alunit

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Alunit
Alunite - USGS Mineral Specimens 015.jpg
Alunite from the Brigham Young University Mineral Collection, Faculty of Geology, Provo, Utah
General and classification
other names
  • Alum stone
  • Alum spar
  • Lœvigit
  • Lœwigite
chemical formula KAl 3 [(OH) 6 | (SO 4 ) 2 ]
Mineral class
(and possibly department) 		Sulfates (and relatives)
System no. to Strunz
and to Dana 		7.BC.10 ( 8th edition : VI / B.11)
02/30/04/01
Crystallographic Data
Crystal system trigonal
Crystal class ; symbol ditrigonal-scalenohedral; 3  2 / m
Space group R 3 m (No. 166)Template: room group / 166
Lattice parameters a  = 6.9741  Å ; c  = 17.190 Å
Formula units Z  = 4
Physical Properties
Mohs hardness 3.5 to 4
Density (g / cm 3 ) measured: 2.6 to 2.9; calculated: 2.82
Cleavage completely after {0001}
Break ; Tenacity clamshell; brittle
colour white, gray, yellowish to reddish
Line color White
transparency transparent to opaque
shine Glass gloss to pearlescent gloss
Crystal optics
Refractive indices n ω  = 1.572
n ε  = 1.592
Birefringence δ = 0.020
Optical character uniaxial positive
Other properties
Chemical behavior insoluble in water and hydrochloric acid
Special features pyroelectric, piezoelectric, red fluorescence (also yellowish white)

Alunite , even alum , Alaunspat , Lœvigit or Lœwigit is a rarely occurring minerals from the mineral class of sulfates (including selenates, tellurates, chromates, molybdates and tungstates), more specifically a basic, anhydrous potassium aluminum sulfate . It crystallizes in the trigonal crystal system with the chemical composition KAl 3 [(OH) 6 | (SO 4 ) 2 ]. Alunit develops either flattened, cube-shaped, rhombohedral crystals or porous, granular aggregates with a white-yellow to reddish color.

Etymology and history

Alunite, derived from alum (from Latin alumen ), was first mined in the 15th century in Tolfa near Rome for alum production under the control of the popes. In 1707 it was described by Jean-Claude Delamétherie as aluminilite , which was then shortened to alunite by François Sulpice Beudant in 1824 . Albrecht Dürer depicted an alunite crystal on his copper engraving Melencolia I (1514).

classification

Alunit already belonged to the mineral class of "sulfates (and relatives)" and there to the department of "anhydrous sulfates, with foreign anions ", where it was named after "Alunit" in the now outdated, but still in use 8th edition of the mineral classification according to Strunz -Group "with the system no. VI / B.11 and the other members Ammonioalunit , Ammoniojarosit , Argentojarosit , Beaverit , Dorallcharit , Huangit , hydronium jarosite , jarosite , Krivovichevit , Minamiit , natroalunite , Natrojarosite , Osarizawait , plumbojarosite and Walthierit 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 Alunit in the category of "Sulphates (selenates, etc.) with additional anions, without H 2 O". However, this is further subdivided according to the relative size of the cations involved , so that the mineral can be found according to its composition in the sub-section “With medium-sized and large cations”, where the “Alunit group” with the system no. 7.BC.10 and the other members ammonioalunite, ammoniojarosite, argentojarosite, beaverite, dorallcharite, huangite, hydronium jarosite, jarosite, minamiite, natroalunite, natrojarosite, osarizawaite, plumbojarosite, locksmithsite and walthierite.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the to the class of "sulfates, chromates and molybdates" and there to the category of "anhydrous sulfates with hydroxyl or halogen". Here it is in the " Alunit group (Alunit sub-group) " with the system no. 02/30/04 within the subsection “Anhydrous sulfates with hydroxyl or halogen with (AB) 2 XO 4 Z q ”.

Crystal structure

Alunit crystallizes in the trigonal crystal system in the space group R 3 m (space group no. 166) with the lattice parameters a  = 6.9741  Å and c  = 17.190 Å as well as four formula units per unit cell . Template: room group / 166

properties

Alunit is a pyroelectric and piezoelectric crystal.

Under UV light , some alunite show a red fluorescence under long wave UV light, a yellowish-white fluorescence was observed.

Education and Locations

Alunit - red, multi-crystalline mineral aggregate

Well-formed single crystals are rarely found in geodes . Alunit crystallizes in a hexagonal system to form trigonal pyramids, which often grow together to form multiple crystals. Chemically, the mineral is a basic potassium aluminum sulfate. If sodium takes the place of potassium, one speaks of soda-alunite, the aluminum is replaced by iron (Fe 3+ ) by jarosite . The latter occurs primarily as a secondary mineral in ores containing iron sulfate. The mineral is insoluble in water and weak acids, but easily soluble in sulphurous acid .

Alunite has so far (as of 2009) been found at around 700 sites, including in Egypt , Argentina , Australia , Bolivia , Brazil , Bulgaria , Chile , China , Costa Rica , Germany , Dominican Republic , Ecuador , Eritrea , Fiji , France , Greece , England , India , Indonesia , Iran , Italy , Japan , Virgin Islands , Canada , Kazakhstan , Kyrgyzstan , Colombia , Madagascar , Morocco , Macedonia , Mexico , Mongolia , Myanmar , New Zealand , Austria , Papua New Guinea , Peru , Philippines , Poland , Romania , Russia , Solomon Islands , Serbia , Slovakia , Spain , South Africa , South Korea , Taiwan , Czech Republic , Turkey , Turkmenistan , Ukraine , Hungary , USA .

use

As a raw material

Alunite is now mined as potassium and aluminum ore . Larger deposits are in Tuscany and Hungary as well as in New South Wales , Colorado , Nevada , Utah and in the Red Mountains in Arizona .

Medical importance

The alum stone has an antiseptic effect (inhibiting and killing pathogens) and astringent (contracting, sealing). It is used as a hemostatic pen to close small wounds that often occur when shaving. It serves as an aftershave for a wet shave and as a preshave for an electric shave.

personal hygiene

Alum stone is an effective and cheap deodorant , free of chemical additives ( irritants , preservatives ) and therefore well tolerated. Slightly moistened over the skin, it reliably binds the molecules that produce the sweat odor (see also Deokristall ).

Speleology (speleology)

Alunit is an aid in determining the age of stalactite caves, as it is deposited on the walls of the cave that forms when groundwater mixed with sulfuric acid penetrates the limestone.

Gemstone

Alunite has recently been used again as a gemstone (mainly cabochon cut). Alunite found in the Austrian Waldviertel is also known as "Bernhardite" (after the place where Bernhard was found ).

See also

literature

Web links

Commons : Alunit  - collection of images, videos and audio files
Wiktionary: Alunit  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ↑ a b c American Mineralogist Crystal Structure Database - Alunite (English, 2006)
  2. ↑ a b Webmineral - Alunite (English)
  3. ↑ a b c d Alunite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( handbookofmineralogy.org [PDF; 67  kB ; accessed on January 20, 2018]).
  4. ↑ a b c Mindat - Alunite (English)
  5. ^ A b Hanna Krejci-Graf, Karl Krejci-Graf: Fluorescent colors of minerals . In: Journal of Crystallography - Crystalline Materials . tape 88 , no. 1-6 , 1934, pp. 260–264 , doi : 10.1524 / zkri.1934.88.1.260 (accessed via De Gruyter Online).
  6. ↑ a b Mineralienatlas: Alunit
  7. ↑ Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 6th completely revised and supplemented edition. Weise, Munich 2014, ISBN 978-3-921656-80-8 .
  8. ↑ Jesús Martínez Fríaz: El enigmático poliedro de Alberto Durero en 'Melancolía I' ( PDF 613 kB )
  9. ↑ Mindat - Number of locations for Alunite
  10. ↑ Brief Info No. 18 of the Austrian Gemmological Society: Alunit - New Gemstone from Austria ( Memento of October 4, 2012 in the Internet Archive ) (PDF 1.9 MB; p. 11)