Sample No: MAC88104, MAC88105

Weight (g): 61.2; 662.5

Dimensions (cm): 4 x 4.5 x 2.5; 11 x 7.5 x 6.5

Location: MacAlpine Hills; MacAlpine Hills

Field No.: 5757; 5759

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 (MAC88105,6) Description: Brain Mason

The section shows a microbreccia of small (up to 3.0 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; one minute grain of metal or metal-sulfide was seen. Some of the clasts consist almost entirely of dark brown semi-opaque glass; others show small plagioclase laths with interstitial glass; one appears to be fine-grained troctolite. Microprobe analyses show that the plagioclase is almost pure anorthite (Na₂O 0.3 - 0.5%, K₂O less than 0.1%). Olivine composition is Fa_10-18; its FeO/MnO ratio is very high, 60 - 80, characteristic of lunar material. The average composition of the glassy matrix is (weight percent): SiO₂ 45, Al₂O₃ 28, FeO 6.3, MgO 4.7, CaO 16, Na₂O 0.36, TiO₂ 0.32, MnO 0.11, K₂O <0.1, i.e. anorthositic. The meteorite is an anorthositic microbreccia, almost certainly of lunar origin.

AMENDED VERSION

Sample No.: MAC88104; 88105

Dimensions (cm): 4x4.5x2.5; 11x7.5x6.5

Weight (g): 61.2; 662.5

Location: MacAlpine Hills

Meteorite Type: Anorthositic Breccia

Field Number: 5757; 5759

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 δ¹⁸O = 5.5, δ¹⁷O = 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

26 Al 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.