Galaxite

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Galaxite
Galaxite-Jacobsite-Wiserite-697074.jpg
Galaxite (reddish brown) with jacobsite (gray-black) from the Kaso Mine, Kanuma , Honshu, Japan (size 11.6 cm × 7.3 cm × 2.0 cm)
General and classification
other names

Manganese spinel

chemical formula Mn 2+ Al 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.01)
02/07/01/02
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  = 8.29  Å
Formula units Z  = 8
Twinning according to {111}, spinel law
Physical Properties
Mohs hardness 7.5
Density (g / cm 3 ) measured: 4.234; calculated: [4.22]
Cleavage indistinct
Break ; Tenacity shell-like
colour black
Line color reddish brown
transparency opaque
shine Glass gloss

Galaxite (also manganese spinel ) is a rarely occurring minerals from the mineral class of " oxides and hydroxides " with the idealized chemical composition Mn 2+ Al 2 O 4 , and thus a chemical point of manganese - aluminate . In nature, however, galaxite is mainly found with small proportions of bivalent iron and magnesium , which replace manganese, and trivalent iron, which partially replace the aluminum in the formula ( substitution ). Therefore, the formula is also given in some sources as (Mn 2+ , Fe 2+ , Mg) (Al, Fe 3+ ) 2 O 4 .

Galaxite crystallizes in the cubic crystal system , but develops only small, mostly rounded crystallites ( grains ) up to about half a millimeter in size, rarely octahedral crystals and crystal twins according to the "spinel law" (interpenetration twins after the octahedral surfaces {111}). In general, the crystals are opaque and black in color with a glass-like sheen on the surfaces. In thin layers and splinters or in transmitted light, these can also be reddish-brown, brownish-orange to deep red or translucent golden-yellow.

Etymology and history

Galaxite was first discovered in the Bald Knob deposit near Sparta in Alleghany County in the US state of North Carolina and described in 1932 by Clarence S. Ross and Paul F. Kerr, who named the mineral after the nearby city of Galax .

classification

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

In the meanwhile outdated, but still in use 8th edition of the mineral systematics according to Strunz , the galaxite belonged to the mineral class of "oxides and hydroxides" and there to the department of "oxides with the molar ratio metal: oxygen = 3: 4", where it belonged together with Hercynite , Gahnit and Spinell the group of "aluminate spinels" with the system no. IV / B.01 .

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 the Galaxit in the category of "Oxides with the molar ratio of metal: oxygen = 3: 4 and comparable". This, however, is further divided according to the size of the participating cations , can be found so that the mineral according to its composition in the subsection "With only medium-sized cations" where it along with Brunogeierit , chromite, Cochromit, Coulsonit, Cuprospinell, Filipstadit , Franklinite, Gahnite, hercynite, jacobsite, magnesiochromite, magnesiocoulsonite, magnesioferrite, magnetite, manganochromite, 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 galaxite to the class of "oxides and hydroxides" and there in the department of "multiple oxides". Here it is together with spinel, hercynite and gahnite in the "aluminum subgroup" with system no. 07.02.01 to be found within the sub-section of " Multiple Oxides (A + B 2+ ) 2 X 4 , Spinel Group ".

Crystal structure

Galaxit crystallizes cubically in the space group Fd 3 m (space group no. 227) with the lattice parameter a  = 8.29  Å and 8 formula units per unit cell . Template: room group / 227

Education and Locations

Galaxite forms in carbonate-rich , silicon dioxide- undersaturated parts of metamorphic manganese deposits . Accompanying minerals include alabandin , alleghanyite , jacobsite , catoptrite , kellyite , kutnohorite , magnetite , magnussonite , manganese humite , manganosite , manganostibite , rhodonite , sonolite , spessartine and tephroit .

As a rare mineral formation, Galaxite has so far only been proven at a few sites, around 40 of which are known. In addition to its type locality , the mineral occurred in the United States at "Corundum Knob" in Clay County (North Carolina) and at Galax , in the "Hutter Mine" and the "Whittles Emery deposit" in Pittsylvania County of Virginia.

The only known site in Germany so far is in the Zeilberg quarry (near Maroldsweisach) in the east of Lower Franconia in Bavaria.

In Switzerland, Galaxit was found in Furtschellas and Tanatz Alp near Splügen GR in the canton of Graubünden as well as on the Pipji glacier near Pipjitälli and at Sparrenflue in the Täschtal in the canton of Valais.

Other locations are in Ghana, Japan (mainly on Honshū ), Namibia, Romania, Russia, Sweden, Thailand and the United Arab Emirates.

See also

literature

  • Clarence S. Ross, Paul F. Kerr: The manganese minerals of a vein near Bald Knob, North Carolina . In: American Mineralogist . tape 17 , 1932, p. 1–18 (English, rruff.info [PDF; 986 kB ; accessed on September 1, 2018]).
  • Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 503 (first edition: 1891).
  • EJ Essene, DR Peacor: Crystal chemistry and petrology of coexisting galaxite and jacobsite and other spinel solutions and solvi . In: American Mineralogist . tape 68 , 1983, pp. 449–455 (English, minsocam.org [PDF; 785 kB ; accessed on September 1, 2018]).

Web links

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

Individual evidence

  1. ↑ 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.  188 .
  2. ↑ a b IMA / CNMNC List of Minerals; March 2018 ( Memento from June 11, 2018 in the Internet Archive ) (PDF 1.65 MB, p. 69)
  3. ↑ Webmineral - Galaxite (English)
  4. ↑ a b c d e Galaxite . 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 August 6, 2018]).
  5. ↑ Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties. Status 03/2018 . 7th, completely revised and supplemented edition. Weise, Munich 2018, ISBN 978-3-921656-83-9 .
  6. ^ Rudolf Jubelt: Minerals. Collecting, determining, occurrence, characteristics . Enke, Stuttgart 1976, ISBN 3-432-89422-8 , pp. 222 .
  7. ↑ 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]).
  8. ↑ Mindat - Number of locations for Galaxite
  9. ↑ Mindat - Galaxite (English)