Graves Nunataks (GRA) 06128 and 06129 (ungrouped achondrite)

Antarctica


description from Antarctic Meteorite Newsletter, Vol. 60, No. 2, August, 2007

Sample No.: GRA 06128; GRA 06129
Location: Graves Nunataks
Field No.: 17918; 17713
Dimensions (cm): 8.5 x 4.0 x 7.5; 8.0 x 5.0 x 2.5
Weight (g): 447.6; 196.450
Meteorite Type: Achondrite Ungrouped

Macroscopic Description: Kathleen McBride

50% of the exteriors has shiny to glassy patches of black fusion crust. The exposed interior is rusty yellow in color and has fractures in a sort of plate-like orientation. The interior has small areas of gray crystalline material. It is a rusty to yellow-ocher color and very weathered.

Thin Section (,2) Description: Tim McCoy, Linda Welzenbach, Glenn MacPherson and Lauren LaCroix

The sections exhibit a granoblastic texture dominated by sodic plagioclase (>70 vol. % in the section studied) with lesser olivine and two pyroxenes, although mafic-rich pockets reaching several mm in size are present. Grain size is very heterogeneous; in one large feldspathic region the crystals are up to 5 mm, but elsewhere are rarely as large as 1 mm, perhaps suggesting formation as a breccia. Minor opaques include ilmenite (1.6% MgO), troilite, Fe,Ni-sulfide (pentlandite; 26% Ni), spinel (13% TiO2, 35% Cr2O3, 3% Al2O3), and Ni-Fe metal (67% Ni) that occurs only as minute inclusions inside of olivine. Silicates are equilibrated with olivine of Fa59, orthopyroxene of Fs44Wo2 (Fe/Mn ≈ 43), clinopyroxene of Fs19Wo43 (Fe/Mn ≈ 30-45) and oligoclase (An14Or2). The combination of its variable grain size, locally granoblastic texture, iron-rich mafics and sodium-rich plagioclase is unlike any known achondrite, including those of planetary origin.

Oxygen isotopic analysis: Z. Sharp, University of New Mexico

Oxygen isotopic analyses of three small (2-5 mg) pieces of GRA 06129 yielded the following results which fall in the Earth, Moon and enstatite meteorite field:

δ17O = 3.04, δ18O = 6.01, Δ18O = -0.09
δ17O = 2.89, δ18O = 5.63, Δ18O = -0.03
δ17O = 3.05, δ18O = 6.01, Δ18O = -0.07

[where Δ18O = δ17O - 0.52 x δ18O]


 

 

GRA 06128 in the field.
Mass of stone: 447.6 g


(Photo stolen from Antarctic Meteorite Location and Mapping Project)

 

GRA 06129 in the field.
Mass of stone: 196.5 g


(Photo stolen from Antarctic Meteorite Location and Mapping Project)

 


Four views of one 334-mg chip of GRA 06128. Click on image for enlargement. All photos to same scale.
Photos by Randy Korotev
   
Four views of one 406-mg chip of GRA 06128. Click on image for enlargement. All photos to same scale.
Photos by Randy Korotev