Lunar Meteorite: MacAlpine Hills 88104 & 88105

paired stones

MAC 88104 and MAC 88105 were found a few minutes apart. This is the bigger stone, MAC 88105. The fusion crust on the 663-gram meteorite is evident in this view. The small cube in the corner is 1 cm on each side. Photo credit: NASA/JSC S89-38379. All of the images here were scanned from photographs in which the colors had shifted. These images have all been color-balanced so that the near face of the 1-cm cube is neutral gray.

**61-gram MAC 88104. Photo credit: from NASA/JSC S89-38376**

Sawn face of MAC 88105. The meteorite is a regolith breccia, i.e., it is composed of compacted regolith or “soil.” Several large, angular clasts are visible in this sawn face. Notice how the fractures run through the clasts as if the clasts are not there. This happens because the clasts and matrix are of equal hardness. This feature is one that distinguishes a lunar breccia from many types of terrestrial sedimentary rocks. Photo credit: NASA/JSC S89-47066)

*Left*: Blue ice, with the MacAlpine Hills in the background. *Right*: The ANSMET88 field team (Robbie Score, Monica Grady, and Scott Sandford) near the collection site. Photo credit: Randy Korotev

Listed in The Meteoritical Bulletin, No. 76

Amended classification from
Antarctic Meteorite Newsletter, Vol. 12, No. 3, 1989 (PDF p. 21)

MacAlpine Hills 88104 & 88105 (MAC 88104 & 88105)

Mass (g): 61.2 (1 piece); 662.5 (1 piece)
Dimensions (cm): 4 x 4.5 x 2.5; 11 x 7.5 x 6.5
Location: MacAlpine Hills, Transantarctic Mountains, Antarctica
Weathering: A/Be; A/Be
Fracturing: A/B; A/B

Meteorite Type: Anorthositic Breccia

Macroscopic Description: Roberta Score. MAC88104 and MAC88105 are paired fragments of a polymict breccia. Both specimens have thin gray-green fusion crust which covers approximately 30% of the exterior surface. The other exterior surfaces are dark gray and weathered, with numerous clasts and vugs where clasts have been plucked out by weathering. A minute amount of evaporite minerals is evident in the minor cracks in the fusion crust. The interior is blue gray and mostly fine-grained, but glassy in some areas. Veins of dark vesicular glass surround some clasts, but do not transect any clasts. The meteorite contains abundant angular feldspathic clasts and fine-grained gray, black and beige clasts. The largest clast exposed (1.5 x 1 cm) is fine-grained and anorthositic, with scattered mafic minerals. Other clasts are medium-grained and more mafic.

Thin Section (MAC88104,7; 88105,6) Description: Brian Mason. The sections show a microbreccia of small (up to 0.3 mm) mineral grains, and clasts (up to 3 mm across), in a translucent to semi-opaque brown glassy matrix. The mineral grains are almost all plagioclase, except for a few olivines and pyroxenes; two pink spinel grains and one minute grain of metal or metal-sulfide were seen in 88105,6. Some of the clasts consist almost entirely of dark-brown semi-opaque glass; others show small plagioclase laths with interstitial glass; some are plagioclase-rich with minor olivine or pyroxene. Microprobe analyses show that the plagioclase is almost pure anorthite (Na₂O 0.3-0.5%, K₂O less than 0.1%). Olivine composition is variable, Fa_10-34; most of the pyroxene is Ca-poor, averaging Wo₆Fs₂₅, but some more Ca-rich grains were analysed; the FeO/MnO ratio is very high, 50-80, characteristic of lunar material. The composition of the glassy matrix is somewhat variable, but averages (weight percent): SiO₂, 45, Al₂O₃ 28, FeO 6.3, MgO 4.7, CaO 16, Na₂O 0.36, TiO₂ 0.32, MnO 0.11, K₂O less than 0.1. The meteorite is an anorthositic microbreccia, almost certainly of lunar origin.

Oxygen Isotopic Composition: Robert Clayton. The oxygen isotopic composition of MAC88105 is d¹⁸O = 5.5, d¹⁷O = 2.7, which falls within the group of previously analyzed lunar meteorites and Apollo lunar rocks.

Thermoluminescence Data: Derek Sears. The measured natural TL values for MAC88104 and MAC88105 are 2.4 +/- 0.3 and 2.9 +/- 0.3 krad at 250 degrees C, respectively. This compares with Steve Sutton’s values of 0.75, 1.7, and 0.5 krad for ALHA81005, YAMATO-791197, and YAMATO-82192, respectively, and with typical values for most Antarctic chondrites of 20-80 krad. These low values reflect recent heating or anomalous (non-classical) fading, observed for some lunar meteorites. (Sutton, 1985, Proc. 10th Symp. Antarctic Meteorites, 133-139: 1986, Meteoritics, 21, 520-521: 1989, personal communications).

²⁶Al Measurement: John Wacker. ²⁶Al activity of MAC88105 is 19.5 ± 2.6 dpm/kg which is considerably lower than the 41-139 dpm/kg measured by Nishiizumi et al. (1988; Meteoritics 23, 294-295) in four other lunar meteorites. The low activity implies either an unreasonably old terrestrial age (>1 MY) or that the sample was heavily shielded on the moon and had a short transit time in space.

Randy Says…

Compositionally, MAC 88104/88105 is a typical feldspathic lunar meteorite. I saw both stones in the field. I thought that they probably were not meteorites. Feldspathic lunar meteorites do not have dark fusion crusts.

More Information

Meteoritical Bulletin Database

MAC 88104 | 88105

Map

ANSMET Location Map

References

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Lunar Meteorites

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