The Muonionalusta iron meteteorite - chemistry and structure

Fine (0.3 mm) Octahedrite classe IVA

Chemical analysis, 8.42% Ni, 2.24 ppm Ga, 0.133 ppm Ge, 1.6 ppm Ir, R. Schaudy et al. (1972).

Something interesting is that the crystal shape (and Widmanstätten figures) seams to be more like tetrahedrons than octahedrons. This has been noticed early by D. Malmqvist (1948).

This could possibly be explained by a shock event, compressing the octahedron to a tetrahedron. Look at the angles at the crystals in this "core specimen". (50x30x15 mm. collection of D. Svensson)


Another "core fragment" showing the angles of a tetrahedron (size 22x17x20 mm).

Something else that indicates some shock event is displacement lines:

Displacement line going through meteorite due to shock event? Click on image for larger hi resolution image. Specimen from D. Svensson collection.

Also the presence of the mineral Stishovite, a high pressure SiO2 (see mineral Table below) is a sign of a possible shock event.

Before the ething procedure the meteorite looks as pure and shiny steel metal, its first after the etchant (nitric acic HNO3, ferric chloride FeCl3 etc) has partly dissolved the polished surface (different minerals dissolve in different amount) that the Widmanstatten pattern occur.


A small mirror polished specimen that has not been etched

Specimen after the etching. Small specimens are more likely to rust to some extension and as you can see on this picture small amounts of rust has occured in small cracks maybee one month after the etching procedure was done, luckily it seems that it has stopped.

Etched meteorite slides look differently depending on the amount of grinding and polishing, the amount and kind of etchant and various different things, this specimen has been prepared in a way making it specially shiny and clear. Specimen measures 40x35 mm. Specimen from D. Svensson collection.

 

Identified minerals:

Very nice troilite inclusion, together with the Troilite other rare minerals sometimes occur. Specimen from collection of T.Österberg.

 

Mineral Chemistry Description (1) Reference
Akaganéite ß-Fe(O,OH,Cl) Brown. D. Holtstam and J. Söderhielm : "The Muonionalusta iron meteorite from Lapland, Sweden : New finds and findings", 5th International Conference "Mineralogy & Museums", Paris, Sept. 5-8th 2004, Bull. de Liaison de la Soc. Franç. de Minéralogie et Cristallographie, 2004, Vol 16, N°2.
Daubreélite FeCr2S4 Metallic, black, greenish-grey.  
Gersdorffite (?) NiAsS Metallic, gray, grayish black.  
Goethite alfa-Fe O(OH) Brown.  
Iron Fe Iron-black D. Holtstam and J. Söderhielm : "The Muonionalusta iron meteorite from Lapland, Sweden : New finds and findings", 5th International Conference "Mineralogy & Museums", Paris, Sept. 5-8th 2004, Bull. de Liaison de la Soc. Franç. de Minéralogie et Cristallographie, 2004, Vol 16, N°2.
Kamacite (Fe,Ni) Metallic grey  
Lepidocrocite gamma-FeO(OH) Sub-metallic, red, reddish-brown  
Magnetite Fe3O4 Metallic greyish black  
Stishovite SiO2   D. Holtstam and J. Söderhielm : "The Muonionalusta iron meteorite from Lapland, Sweden : New finds and findings", 5th International Conference "Mineralogy & Museums", Paris, Sept. 5-8th 2004, Bull. de Liaison de la Soc. Franç. de Minéralogie et Cristallographie, 2004, Vol 16, N°2.
Taenite (Fe,Ni) Greyish white  
Troilite FeS    

1. www.mindat.org (2005-07-09)

©2005 Daniel Svensson E-mail: admin@muonionalustameteorites.com or daniel_svensson@hotmail.com