Zinc chromite

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Zinc chromite
Zincochromite.jpg
Zincochromite platelets, embedded in an acrylic carrier from the UV deposit Srednyaya Padma , Republic of Karelia , Russian Federation
General and classification
other names

IMA 1986-015

chemical formula ZnCr 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.04)
02/07/03/06
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  = 8.35  Å
Formula units Z  = 8
Physical Properties
Mohs hardness 6 ( VHN = 620)
Density (g / cm 3 ) calculated: 5.434
Cleavage is missing
colour brownish black, in transmitted light brown, reflection color brownish gray
Line color brown
transparency opaque, translucent in thin splinters
shine Semi-metallic luster
magnetism weak paramagnetic

Zincochromite is a very seldom occurring mineral from the group of spinels within the mineral class of "oxides and hydroxides" with the idealized chemical composition ZnCr 2 O 4 and thus chemically a zinc - chromium - oxide . It is also the zinc analogue of chromite (Fe 2+ Cr 2 O 4 ).

Zincochromite crystallizes in the cubic crystal system , but develops only tiny, octahedral crystals up to about 0.05 mm in size, brownish-black in color with a semi-metallic sheen on the surfaces. The mineral is generally opaque and translucent brownish only in thin splinters. In the incident light microscope , zinc chromite appears brownish-gray with brownish internal reflections. His line color , however, is always brown.

Etymology and history

Was first discovered Zincochromit in the uranium - vanadium - deposit Srednyaya Padma ( Russian Средняя Падма ) of Velikaya Guba ( Russian Великая Губа ) near the eponymous river Padma on Lake Onega in the peninsula Zaonezhie ( Russian Заонежский ) in the Russian Federation belonging to the Republic of Karelia . The first description was in 1987 by AR Nesterov and Ye. V. Rumyantseva, who named the mineral based on its main component zinc and its relationship to chromite .

The type material of the mineral is in the State Mining University of Saint Petersburg (formerly Mining Institute ) under the catalog no. 1238/1 kept.

classification

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

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

The 9th edition of Strunz's mineral systematics, which has been in effect since 2001 and is used by the IMA, also classifies zincochromite 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, manganochromite, nichromite (N), qandilite , spinel, trevorite, ulvöspinell and vuorelainenite 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 zincochromite to the class of “oxides and hydroxides” and there in the “multiple oxides” section. Here it is together with chromite, cochromite, magnesiochromite, manganochromite and nichromite 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 ZnCr 2 O 4 consists of 28.02% zinc (Zn), 44.56% chromium (Cr) and 27.42% oxygen (O). In the oxide form, this corresponds to 34.87% ZnO and 65.13% Cr 2 O 3 . The analyzed samples from the Velikaya Guba type locality , however, also contained a significant proportion of V 2 O 3 between 1.42% and 7.67%, Fe 2 O 3 between 1.36% and 4.21%, and Al 2 O 3 between 0.51% and 1.44% and SiO 2 between 2.44% and 3.36% (all data in% by weight). In addition, there is a small proportion of up to 0.82% TiO 2 . On the basis of four oxygen atoms, the empirical formula for Zn 1.04 (Cr 1.61 V 0.11 Si 0.11 Fe 3+ 0.06 Al 0.05 ) = 1.94 O 4 is calculated .

Crystal structure

Zincochromite crystallizes cubically in the spinel structure with the space group Fd 3 m (space group no. 227) , the lattice parameter a  = 8.35  Å and 8 formula units per unit cell . Template: room group / 227

properties

Zincochromite is paramagnetic .

Education and Locations

Zincochromite forms in Cr- and V-rich and mica-containing metasomatites by displacing chromium-containing aegirins in the fracture zones of metamorphosed sedimentary rocks . In addition to aegirine, quartz and various Cr-V-Fe oxides and hydroxides occur as accompanying minerals .

Zincochromite is one of the very rare mineral formations and could therefore only be discovered in a few samples from less than 10 known sites (as of 2018). Within the Russian Federation, in addition to its type locality Velikaya Guba , zincochromite occurred in the nearby Srednyaya Padma mine (also a uranium-vanadium deposit) on the Zaonezhie peninsula in the Republic of Karelia and in the Chudnoe palladium-gold deposit in the Maldynyrd Mountains in the Komi Republic .

The only known site in Austria so far are the serpentinites on the northern flank of the Brennkogel in the border area between Carinthia and the Salzburg region .

Other well-known sites are the Dolo Hills in Young Shire in the Australian state of New South Wales, the Kuikkapuro deposit near Suomussalmi in Finland, the Tarkwa gold mine in Ghana, some volcanic mineral samples from the Mahanadi riverside in the Indian state of Odisha , the dolomite marbles in the Babuna Valley (Jakupica Mountains) near Nežilovo in Macedonia and a soap deposit on the Quebrada Grande River near Guaniamo in the state of Bolívar in Venezuela.

See also

literature

  • AR Nesterov, Ye. V. Rumyantseva: Zincochromite Zn Cr 2 O 4 - A new mineral from Karelia . In: Zapiski Vsesoyuznogo Mineralogicheskogo Obshchestva . tape 116 , no. 3 , 1987, pp. 367-371 (Russian).
  • John Leslie Jambor , Kenneth W. Bladh, T. Scott Ercit, Joel D. Grice, Edward S. Grew: New Mineral Names . In: American Mineralogist . tape 73 , no. 7-8 , 1988, pp. 927-935 ( minsocam.org [PDF; 1,2 MB ; accessed on September 7, 2018]).
  • H. St. C. O'Neill, WA Dollase: Crystal Structures and Cation Distributions in Simple Spinels from Powder XRD Structural Refinements: MgCr 2 O 4 , ZnCr 2 O 4 , Fe 3 O 4 and the Temperature Dependence of the Cation Distribution in ZnAl 2 O 4 . In: Physics and Chemistry of Minerals . tape 20 , no. 8 May 1994, pp. 541-555 , doi : 10.1007 / BF00211850 .
  • 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. 303 .
  • Igor V. Pekov: Minerals first discovered on the territory of the former Soviet Union . 1st edition. Ocean Pictures, Moscow 1998, ISBN 5-900395-16-2 , pp. 241-242 .
  • Davide Levy, Valeria Diella, Alessandro Pavese, Monica Dapiaggi, Alessandra Sani: PV equation of state, thermal expansion, and PT stability of synthetic zincochromite (ZnCr2O4 spinel) . In: American Mineralogist . tape 90 , 2005, pp. 1157–1162 ( rruff.info [PDF; 209 kB ]).
  • Zdenek Johan, Daniel Ohnenstetter: Zincochromite from the guaniamo river diamondiferous placers, Venezuela: Evidence of its metasomatic origin . In: The Canadian Mineralogist . tape 48 , 2010, p. 501-514 , doi : 10.3749 / canmin.48.2.000 .

Web links

Commons : Zincochromite  - Collection of Images

Individual evidence

  1. ↑ a b c 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 Webmineral - Zincochromite (English)
  4. ↑ a b c d 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 .
  5. ↑ a b c d Zincochromites . 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; 69  kB ; accessed on September 7, 2018]).
  6. ^ A b 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. 303 .
  7. ^ Igor V. Pekov: Minerals first discovered on the territory of the former Soviet Union . 1st edition. Ocean Pictures, Moscow 1998, ISBN 5-900395-16-2 , pp. 241-242 .
  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. ↑ John Leslie Jambor , Kenneth W. Bladh, T. Scott Ercit, Joel D. Grice, Edward S. Grew: New Mineral Names . In: American Mineralogist . tape  73 , no. 7-8 , 1988, pp. 927-935 ( minsocam.org [PDF; 1,2 MB ; accessed on September 7, 2018]).
  10. ↑ Mindat - Number of localities for zincochromites (English)
  11. ↑ Find location list for zincochromite in the Mineralienatlas and Mindat