Dufrénit

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Dufrénit
Dufrenite-235235.jpg
Dufrénit, location: Wheal Phoenix
General and classification
chemical formula Ca 0.5 Fe 2+ (Fe 3+ ) 5 (PO 4 ) 4 (OH) 6 · 2 H 2 O
Mineral class
(and possibly department) 		Phosphates, arsenates, vanadates
System no. to Strunz
and to Dana 		8.DK.15 ( 8th edition : VII / D.11)
42.09.01.02
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group C 2 / c (No. 15)Template: room group / 15
Lattice parameters a  = 25.84  Å ; b  = 5.126 Å; c  = 13.78 Å
β  = 111.20 °
Formula units Z  = 4
Physical Properties
Mohs hardness 3.5 to 4.5
Density (g / cm 3 ) 3.1 to 3.34
Cleavage Well
Break ; Tenacity uneven
colour dark green, brown, black
Line color gray green, light gray
transparency translucent to opaque
shine Glass gloss, matt
Crystal optics
Refractive indices n α  = 1.820 to 1.842
n β  = 1.830 to 1.850
n γ  = 1.875 to 1.925
Birefringence δ = 0.055 to 0.083
Optical character alternating biaxially

Dufrénit (also Grüneisenstein , Grüneisenerz , Kraurit or Metanochlor ) is a rarely occurring mineral from the mineral class of phosphates (arsenates, vanadates) with the chemical composition Ca 0.5 Fe 2+ (Fe 3+ ) 5 (PO 4 ) 4 ( OH) 6 · 2 H 2 O.

Dufrénit crystallizes in the monoclinic crystal system and develops mostly microcrystalline, spherical, grape-like to kidney-shaped aggregates with a radial fiber texture and dark green, brown or black color.

Etymology and history

Dufrénit was first described in 1833 by Alexandre Brongniart , who named the mineral after the French geologist and mineralogist Armand Dufrénoy . The type locality is the "Grube Hoff Auf Mich" near Ullersreuth / Hirschberg (Saale) in Thuringia.

classification

In the old (8th edition) and new systematics of minerals according to Strunz (9th edition) , Dufrénit belongs to the department of "water-containing phosphates with foreign anions ". The new Strunz'sche mineral classification, however, subdivides here more precisely according to the size of the cations and the mineral is therefore correspondingly in the sub-section “With large and medium-sized cations; (OH etc.): RO 4  > 1: 1 and <2: 1 “.

The systematics of minerals according to Dana sorts the Dufrénit into the division of "water-containing phosphates etc., with hydroxyl or halogen " and there into the sub-division "with (A) 3 (XO 4 ) 2 Z q  • x (H 2 O)"

Crystal structure

Dufrénite crystallizes in the monoclinic crystal system in the space group C 2 / c (space group no. 15) with the lattice parameters a  = 25.84  Å ; b  = 5.126 Å, c  = 13.78 Å and β = 111.20 ° as well as four formula units per unit cell . Template: room group / 15

Education and Locations

Dufrénit forms as a secondary mineral in granitic pegmatite by hydrothermal conversion of other phosphate minerals as well as in the oxidation zone of iron - deposits .

So far, the mineral has been found in 97 locations (as of 2009), including in Córdoba and San Luis (Argentina); New South Wales , Northern Territory , South Australia , Victoria and Western Australia (Australia); Minas Gerais (Brazil); in brown iron ore in Siegerland , near Waldgirmes , Hirschberg (Saale) , Hauptmannsgrün in Vogtland (Germany); Auvergne , Brittany , Limousin and Poitou-Charentes (France); Attica (Greece); England (Great Britain); Honshū (Japan); Erongo and Tsumeb (Namibia); Viseu (Portugal); Sweden ; South Africa ; Spain ; Bohemia (Czech Republic); as well as many regions in the US .

See also

literature

  • Petr Korbel, Milan Novák: Encyclopedia of Minerals . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 163 .
  • Dufrénite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 68 kB )

Web links

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

Individual evidence

  1. ↑ a b c Webmineral - Dufrénite (English)
  2. ↑ a b c American Mineralogist Crystal Structure Database - Dufrénite (English)
  3. ↑ a b c d Mindat - Dufrénite (English)
  4. ↑ IMA / CNMNC List of Mineral names - Dufrénite (English, PDF 1.8 MB, p. 76)
  5. ↑ Find location list for Dufrénit in the Mineralienatlas and Mindat