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Allan Hills A81001
Basic information Name: Allan Hills A81001
     This is an OFFICIAL meteorite name.
Abbreviation: ALHA81001
This meteorite may also be called Allan Hills 81001 (ALH 81001) in publications.

Observed fall: No
Year found: 1981
Country: Antarctica [Collected by US Antarctic Search for Meteorites program (ANSMET)]
Mass:help 52.9 g
Classification
  history:
Antarctic Meteorite Newsletter:  AMN 6(1)  (1983)  Eucrite-an
AMN 13(1)  (1990)  Eucrite-pmict?
AMN 17(1)  (1994)  Eucrite-pmict
Meteoritical Bulletin:  MB 76  (1994)  Eucrite-pmict
NHM Catalogue:  5th Edition  (2000)  Eucrite-pmict
MetBase:  v. 7.1  (2006)  Eucrite-mmict
Antarctic Meteorite Newsletter:  AMN 33(1)  (2010)  Eu "ub"
Recommended:  Eucrite-unbr    [explanation]

This is 1 of 92 approved meteorites classified as Eucrite-unbr.   [show all]
Search for other: Achondrites, Eucrites, and HED achondrites
Writeuphelp
Writeup from AMN 6(1):

Sample No.: ALHA81001

Location: Allan Hills

Field No.: 1505

Weight (gms): 52.9

Meteorite Type: Eucrite (anomalous)

Physical Description: Roberta Score

This achondrite is covered on two surfaces with a shiny black fusion crust. The interior appears massive and is a smokey gray color. Many cracks penetrate the interior of this meteorite. After drying in a nitrogen cabinet for several hours, a minute amount of white deposit lines one crack. Dimensions: 4.5 x 4.0 x 4.5 cm.

 

Petrographic Description: Brian Mason

The section is translucent in pale brown-gray, with some darker areas, giving a patchy appearance. With crossed polars the material is seen to consist of pyroxene prisms up to 0.5 mm long, mostly with straight extinction, in a glassy groundmass. No opaque minerals are present. Microprobe analyses show the pyroxene has rather uniform composition, averaging Wol.6En40Fs59 , with 0.4% A12O3, 0.2% TiO2, 0.9% MnO, and 0.6% Cr2O3. Broad-beam analyses give an approximate bulk composition (weight percent) as follows: SiO2 49, Al2O3 14, FeO 18, MgO 6.7, CaO 10, Na2O 0.2, K2O <0.1, TiO2 0.9, Cr2O3 0.6, MnO 0.7. This composition agrees with that of an average eucrite, except that Na2O is lower (in most eucrites Na2O is about 0.5%); however, the texture is quite different from any described eucrite. The overall impression from the texture is that the material represents a rapidly quenched melt.


Writeup from AMN 33(1):
ALHA81001 original classification in AMN 6, no. 1, as an anomalous eucrite. Later reclassified in AMN 17, no. 1, as a polymict eucrite. Numerous thin sections reveal no brecciation and subsequent chemical and textural studies [1, 2, 3] all suggest reclassification as unbrecciated eucrite.

[1] P.H.Warren et al., Papers 21st Symp. Ant. Met., NIPR Tokyo, 1996, p.195
[2] Mittlefehldt, D.W., and Lindstrom, M.M. (2003) Geochemistry of eucrites: Genesis of basaltic eucrites, and Hf and Ta as petrogenetic indicators for altered Antarctic eucrites. Geochimica et Cosmochimica Acta, 67, no. 10, 1911-1935.
[3] Mayne, R.G., McSween, Jr., H.Y., McCoy, T.J., and Gale, A., (2009) Petrology of the unbrecciated eucrites. Geochimica et Cosmochimica Acta, 73, 794-819.
Data from:
  MB76
  Table 2
  Line 524:
Origin or pseudonym:Main icefield
Mass (g):52.9
Class:Eu "pm"
Weathering grade:Ae
Ferrosilite (mol%):59
Catalogs:
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References: Published in Antarctic Meteorite Newsletter 33(1) (2010), JSC, Houston
Published in Antarctic Meteorite Newsletter 6(1) (1983), JSC, Houston
Published in Meteoritical Bulletin, no. 76, Meteoritics 29, 100-143 (1994)
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Geography:

Antarctica
Coordinates:
     Catalogue of Meteorites:   (76° 43'S, 159° 40'E)
     Recommended::   (76° 42' 4"S, 159° 24' 11"E)
Note: the NHM and MetBase coordinates are 7 km apart

Statistics:
     This is 1 of 39173 approved meteorites from Antarctica (plus 5051 unapproved names)
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