Iowait

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Iowait
Iowaite-605914.jpg
Group of tabular Iowaite crystals from the Palabora Mine, Loolekop , Limpopo Province , South Africa (size: 1.4 cm × 0.9 cm × 0.2 cm), connected on both sides
General and classification
other names

IMA 1967-002

chemical formula Mg 6 Fe 3+ 2 (OH) 16 Cl 2 · 4H 2 O
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.FL.05 ( 8th edition : IV / F.05)
04/06/05/01
Crystallographic Data
Crystal system trigonal
Crystal class ; symbol ditrigonal- scalenohedral ; 3 m
Room group (no.) R 3 m (No. 166)
Lattice parameters a  = 3.12  Å ; c  = 24.11 Å
Formula units Z  = 8
Physical Properties
Mohs hardness 1.5 to 2.5
Density (g / cm 3 ) measured: 2.09; calculated: 2.04
Cleavage completely after {0001}
Break ; Tenacity waxy, fragile after a while on contact with air
colour bluish green to light green with a rusty red tinge, yellowish to colorless
Line color White
transparency translucent to opaque
shine Greasy shine
Crystal optics
Refractive indices n ω  = 1.543 to 1.561
n ε  = 1.533 to 1.543
Birefringence δ = 0.010 to 0.018
Optical character uniaxial negative
Other properties
Special features gives a greasy or soapy feeling on skin contact

Iowaite is a very rarely occurring mineral from the mineral class of " oxides and hydroxides ". It crystallizes in the trigonal crystal system with the chemical composition Mg 6 Fe 3+ 2 (OH) 16 Cl 2 · 4H 2 O, so it is a hydrous magnesium - iron - chlorine hydroxide.

Iowait develops tabular crystals up to about 2.5 centimeters in size, which are usually connected to mica-like layers, but also occurs in the form of massive mineral aggregates . The surfaces of the usually opaque and only translucent crystals at the edges have a fat-like sheen . Fresh mineral samples in decomposed serpentinites are initially bluish-green in color, but over time they turn into light green with a tinge of rust red due to further weathering and conversion to pyroaurite . Yellowish or colorless Iowaites are also rarely found.

With a Mohs hardness of 1.5 to 2.5, Iowaite is one of the soft minerals that, like the reference minerals talc (Mohs hardness: 1) and gypsum (Mohs hardness: 2), can be scratched with the fingernail. When it comes into contact with the skin, the soft mineral therefore also has a greasy or soapy feeling.


Etymology and history

Was first discovered in iowait rock samples a serpentinite - core from Precambrian time in about 1000-1500  feet (about 304.8 to 457.2 m) were taken depth. The unnamed test hole was drilled in Sioux County , Iowa . It was described in 1967 by Donald W. Kohls and John Landon Rodda, who named the mineral after the state in which its type locality is located.

Type material of the mineral is kept in the National Museum of Natural History in Washington, DC, USA (catalog no. 121706).

classification

Already in the outdated, but partly still in use 8th edition of the mineral systematics according to Strunz , the Iowaite belonged to the mineral class of "oxides and hydroxides" and there to the department of "hydroxides and oxidic hydrates (water-containing oxides with a layered structure)", where it belongs together with chloromagaluminite , Fougèrit , meixnerite , muskoxite and woodallite formed the unnamed group IV / F.05 .

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), classifies the Iowait under the category of "hydroxides (without V or U )". This is further subdivided according to the possible presence of additional water of crystallization (H 2 O) and the crystal structure , so that the mineral is classified in the sub-section “Hydroxides with H 2 O ± (OH); Layers of edge-linked octahedra "can be found, where together with akdalaite , fougèrit, jamborite , meixnerite, muskoxite and woodallite the" meixnerite group "with the system no. 4.FL.05 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Iowait to the class of "oxides and hydroxides" and there in the category of "hydroxides and hydroxides containing oxides". Here it can only be found together with woodallite in the unnamed group 06.04.05 within the sub-section " Hydroxides and hydroxy-containing oxides with various cations ".

Education and Locations

Close-up of leafy Iowaite crystals from the Palabora Mine, South Africa (15 mm field of view)

Iowaite forms as a secondary weathering product from serpentine and even weathers after some time in the air to pyroaurite . As accompanying minerals in addition to the mentioned among other Antigorit various apatites , brucite , calcite , Chondrodite , chrysotile , Celestine , dolomite , Fluoborit , hydrotalcite , Clinochlore , magnesite , magnetite , phlogopite and pyrite occur.

Iowait is one of the very rare mineral formations due to its little more than 10 known sites (as of 2014). Its type locality , the unnamed test well in Sioux County of Iowa, is the only known site in the United States to date .

The mineral was also found in the Jeffrey Mine near Asbestos ( Les Sources municipality , Québec) in Canada; near Zawiercie (Silesian Voivodeship) in Poland; near Zheleznogorsk-Ilimski (Irkutsk Oblast), Daldyn ( Sakha , Yakutia ), Norilsk (Krasnoyarsk Region) and Ust-Koksa (Altai) in Russia; near Olmaliq ( Almalyk ) in the Uzbek province of Tashkent; Found in the Palabora Mine near Loolekop in the South African province of Limpopo and at a few sites in the vicinity of the Centipede Lake Way uranium deposit and on Mount Keith in Western Australia .

Iowait could also be detected in rock samples from the Pacific Ocean , more precisely from the Mariana Forearc Basin from the "DSDP 778" borehole.


Crystal structure

Iowait crystallizes trigonal in the space group R 3 m (space group no. 166) with the lattice parameters a  = 3.12  Å and c  = 24.11 Å ° with 3/8 formula units per unit cell .

See also

literature

  • DW Kohls, JL Rodda: Iowaite, a new hydrous magnesium hydroxide-ferric oxychloride from the Precambrian of Iowa. In: American Mineralogist. Volume 52 (1967), pp. 1261–1271 ( PDF 614.6 kB )
  • RSW Braithwaite, Pete J. Dunn, RG Pritchard, WH Paar: Iowaite, a re-investigation. In: Mineralogical Magazine. Volume 58 (1994), pp. 79-85 ( PDF 455.2 kB )
  • SJ Mills, AG Christy, J.-MR Génin, T. Kameda, F. Colombo: Nomenclature of the hydrotalcite supergroup: natural layered double hydroxides. In: Mineralogical Magazine. Volume 76 (2012), pp. 1289-1336 doi : 10.1180 / minmag.2012.076.5.10
  • Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke , Stuttgart 1978, ISBN 3-432-82986-8 , pp. 551 (first edition: 1891).
  • Hans Jürgen Rösler : Textbook of Mineralogy . 4th revised and expanded edition. German publishing house for basic industry (VEB), Leipzig 1987, ISBN 3-342-00288-3 , p. 424 .

Web links

Commons : Iowaite  - collection of pictures, 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.  243 .
  2. ↑ a b c d Iowaite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 70.6 kB )
  3. ↑ a b Mindat - Iowaite
  4. ^ DW Kohls, JL Rodda: Iowaite, a new hydrous magnesium hydroxide-ferric oxychloride from the Precambrian of Iowa. In: American Mineralogist. Volume 52 (1967), pp. 1261–1271 ( PDF 614.6 kB )
  5. ↑ Mindat - Number of localities for Iowait
  6. ↑ Find location list for Iowait at the Mineralienatlas and at Mindat
  7. ↑ Mindat - type locality DSDP hole 778, Mariana forearc, Pacific Ocean