Manganochromite

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Manganochromite
Manganochromite-642284 (cropped) .jpg
Submicroscopic intergrowth of manganochromite in pyrrhotite from the Sätra mine, Erzfeld Doverstorp, Östergötland County , Sweden (size 25 mm × 25 mm × 30 mm)
General and classification
other names

IMA 1975-020

chemical formula
  • Mn 2+ Cr 2 O 4
  • (Mn 2+ , Fe 2+ ) (Cr 3+ , V 3+ ) 2 O 4
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.BB.05 ( 8th edition : IV / B.03)
02/07/03/02
Crystallographic Data
Crystal system cubic
Crystal class ; symbol cubic hexakisoctahedral; 4 / m  3  2 / m
Space group Fd 3 m (No. 227)Template: room group / 227
Lattice parameters a  = 8.47  Å
Formula units Z  = 8
Physical Properties
Mohs hardness 6 to 6.5 ( VHN 20 = 1000 ± 70)
Density (g / cm 3 ) calculated: 4.86 to 4.90
Cleavage is missing
colour gray-black, brownish-gray in incident light
Line color not defined
transparency translucent
shine Metallic luster

Manganochromite is a very seldom occurring mineral from the group of spinels within the mineral class of "oxides and hydroxides" with the chemical composition Mn 2+ Cr 2 O 4 and therefore chemically a manganese - chromium - oxide .

Manganochromite crystallizes in the cubic crystal system , but has so far only been found in the form of microcrystalline grains between 10  μm and 80 μm × 800 μm. The mineral is translucent and shows a metallic sheen on the surfaces of the gray-black, and brownish-gray grains under the incident light microscope .

Manganochromite forms a mixed crystal row with vuorelainenite (Mn 2+ V 3+ 2 O 4 ) .

Etymology and history

Was first discovered in the former Manganochromit pyrite - Quarry Shepherd Hill , about 3.5 km north-northeast of Neirne 47 km, east of Adelaide , the Mount Lofty Ranges of South Australia in Australia. The first description was in 1978 by James Graham (1929-2001), who named the mineral based on its main component manganese and its relationship with magnesiochromite .

The type material of the mineral is in the Western Australian Museum in Perth under the catalog no. M.65.1991 kept.

classification

The current classification of the International Mineralogical Association (IMA) is one of the Manganochromit to spinel supergroup , where he together with chromite , Cochromit , Coulsonit , Cuprospinell , Franklinite , Gahnit , Galaxit , Hercynit , Jakobsit , Magnesiochromite , Magnesiocoulsonit , Magnesioferrit , magnetite , spinel , Trevorit , Vuorelainenit and Zincochromit forming the spinel subgroup within the Oxispinelle.

Already in the outdated, but still in use 8th edition of the mineral classification according to Strunz , the manganochromite belonged to the mineral class of "oxides and hydroxides" and there to the department of "oxides with a molar ratio of metal: oxygen = 3: 4 (spinel type M 3 O 4 and related Compounds) ", where together with chromite, cochromite, magnesiochromite, nichromite and zincochromite, the group of" chromite spinels "with the system no. IV / B.03 .

The 9th edition of Strunz's mineral systematics, which has been in force since 2001 and is used by the IMA, also classifies manganochromite in the oxides division with a molar ratio of “metal: oxygen = 3: 4 and comparable”. This, however, is further divided according to the relative size of the participating cations , is so that the mineral according to its composition in the subdivision to find "With only medium-sized cations" where it along with Brunogeierit , chromite, Cochromit, Coulsonit, Cuprospinell, Filipstadit , Franklinite, Gahnite, galaxite, hercynite, jacobsite, magnesiochromite, magnesiocoulsonite, magnesioferrite, magnetite, nichromite (N), qandilite , spinel, trevorite, ulvöspinell , vuorelainenite and zincochromite the "spinel group" with the system no. 4.BB.05 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the manganochromite to the class of "oxides and hydroxides" and there in the section "multiple oxides". Here it is together with chromite, cochromite, chromite, nichromite and zinc chromite in the " chrome subgroup " with the system no. 07.02.03 can be found in the subsection “Multiple oxides (A + B 2+ ) 2 X 4 , spinel group”.

Chemism

The idealized, theoretical compound Mn 2+ Cr 2 O 4 consists of 24.64% by weight of manganese (Mn), 46.65% by weight of chromium (Cr) and 28.71% by weight of oxygen (O).

In the examined samples from the type locality Shepherd Hill, however, small admixtures of vanadium , iron and zinc were found . On the basis of four oxygen atoms, the empirical formula is calculated as follows: (Mn 0.77 Fe 0.30 Zn 0.05 ) Σ = 1.12 (Cr 1.88 V 0.04 ) Σ = 1.92 O 4 . Comparative samples from the Sätra mine in Sweden also contained titanium , which leads to the slightly different empirical formula (Mn 0.83 Fe 0.17 Zn 0.02 ) Σ = 1.02 (Cr 1.06 V 0.92 Ti 0.01 ) Σ = 1.99 O 4 .

The resulting idealized mixed formula is accordingly (Mn 2+ , Fe 2+ ) (Cr 3+ , V 3+ ) 2 O 4 . The elements manganese and iron or chromium and vanadium specified in the round brackets can represent each other in the formula ( substitution , diadochy), but are always in the same proportion to the other components of the mineral.

Crystal structure

Manganochromite crystallizes cubically in the spinel structure with the space group Fd 3 m (space group no. 227) , the lattice parameter a  = 8.47  Å and 8 formula units per unit cell . Template: room group / 227

Education and Locations

Manganochromite is one of the very rare mineral formations that have so far only been known in a few samples. Its type locality Shepherd Hill in South Australia is the only known site in Australia so far. The deposit consists of sedimentary , pyrite- rich layers and was formed during the Cambrian . Manganochromite is found there in paragenesis with pyrrhotite , rutile and diopside .

In the Vourinos Mountains in the Greek region of Western Macedonia , manganochromite appeared as a component of the ophiolites found there. The related spinels chromite and magnetite as well as some rare element minerals such as Awaruit , solid copper , rutheniridosmin as well as iridium and osmium in the Osmiridium variety were found here as accompanying minerals .

In the Sätra iron ore mine , a pyrite- pyrrhotite deposit of the Fahlband type in the Doverstorp ore field near Finspång in Sweden, the mineral was found in association with vuorelainenite , sphalerite and alabandin .

In Spain in El Molar in the province of Tarragona lying Mina Serrana is a manganese ore deposits formed by contact metamorphism was, next to Manganochromit other manganese minerals as in, among other manganite , Manganocummingtonite , Manganogrunerit , Pyroxmangit and Rhodochrosit found.

On Olkhon bottleneck near Lake Baikal in Russia's Irkutsk Oblast , also known as type locality of the previously discovered only there Minerals Olkhonskit applies to Manganochromit found, among other things, along with the also very rare minerals Berdesinskiit , eskolaite , Karelianit , Schreyerit and Vuorelainenit.

In addition, manganochromite was found together with alabandin, daubréelite , olivine , pyroxene , troilite and various zinc sulfides in the iron meteorite Burkhala , which was found in Russia in 1983.


See also

literature

  • J. Graham: Manganochromite, palladium antimonide, and some unusual mineral associations at the Nairne pyrite deposit, South Australia . In: American Mineralogist . tape 63 , no. 11-12 , 1978, pp. 1166 ( minsocam.org [PDF; 978 kB ; accessed on September 3, 2018]).
  • Richard V. Gaines, H. Catherine W. Skinner, Eugene E. Foord, Brian Mason , Abraham Rosenzweig: Dana's New Mineralogy . 8th edition. John Wiley & Sons, New York (et al.) 1997, ISBN 0-471-19310-0 , pp. 301-302 .
  • Giovanni Grieco, Anna Merlini: Chromite alteration processes within Vourinos ophiolite . In: International Journal of Earth Sciences . tape 101 , no. 6 , September 2011, p. 1–11 , doi : 10.1007 / s00531-011-0693-8 ( researchgate.net [PDF; 825 kB ; accessed on September 5, 2018]).

Web links

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

Individual evidence

  1. ↑ a b IMA / CNMNC List of Mineral Names; March 2018 (PDF 1.65 MB)
  2. ↑ a b c d e Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  189 (English).
  3. ↑ a b c 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 .
  4. ↑ a b c d e f g Manganochromite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 67  kB ; accessed on September 3, 2018]).
  5. ↑ Webmineral - Manganochromite (English)
  6. ^ A b c J. Graham: Manganochromite, palladium antimonide, and some unusual mineral associations at the Nairne pyrite deposit, South Australia . In: American Mineralogist . tape 63 , no. 11-12 , 1978, pp. 1166 (English, minsocam.org [PDF; 978 kB ; accessed on September 3, 2018]).
  7. ^ Mineralienatlas : Type locality Shepard Hill Quarry
  8. ↑ Cristian Biagioni, Marco Pasero: The systematics of the spinel-type minerals: An overview . In: American Mineralogist . tape 99 , no. 7 , 2014, p. 1254–1264 , doi : 10.2138 / am.2014.4816 (English, preliminary version online [PDF]).
  9. ↑ a b c d List of places where manganochromite was found in the Mineralienatlas and Mindat
  10. ↑ Mindat - mineral locality Vourinos Mountain Ophiolithkomplex (English)
  11. ↑ Meteoritical Bulletin Database - Burkhala (English)