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| Lewis Cliff 88774 | |||||||||||||||||||||||||
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| Basic information | Name: Lewis Cliff 88774 This is an OFFICIAL meteorite name. Abbreviation: LEW 88774 Observed fall: No Year found: 1988 Country: Antarctica [Collected by US Antarctic Search for Meteorites program (ANSMET)] Mass:  3.1 g | ||||||||||||||||||||||||
| Classification history: |
This is 1 of 7 approved meteorites classified as Ureilite-an. [show all] Search for other: Achondrites, Ureilites | ||||||||||||||||||||||||
| Comments: | Field number: 5323 | ||||||||||||||||||||||||
| Writeup |
Writeup from AMN 16(1):
Sample No.: LEW88774 Location: Lewis Cliff Dimensions (cm): 1.2 x 1.3 x 0.8 Weight (g): 3.1 Meteorite Type: Ureilite
Macroscopic Description: Cecilia Satterwhite Approximately half of the exterior of LEW88774 is covered with weathered brown fusion crust. Weathering of this stone has masked most of its characteristics, but its crystalline nature is still preserved.
Thin Section (,2) Description: Brian Mason and Glenn MacPherson Visual inspection of the thin section shows a very uneven polish, owing to the presence of millimeter-sized opaque black regions that stand out in positive relief next to the silicate matrix.
Petrographic examination shows that this stone is dominated by large (up to ~4 mm) twinned low-Ca pyroxene grains with coarse exsolution lamellae of augite, accompanied by subordinate opaque-fringed olivine crystals (up to ~1 mm), abundant red-brown translucent Cr-spinel crystals, some interstitial metal associated with the spinel, and large carbonaceous areas that apparently consist of graphite (bireflective) enclosing diamond. Light reddish-yellow staining in thin section indicates mild terrestrial weathering; iron oxide was identified in interstitial veins.
Analyses of the constituent phases gave the following compositions: olivine crystals have cores of Fa21-25 rimmed by narrow zones of Fa4-6 plus iron metal; Low-Ca pyroxene grains have cores of Wo4-5Fs20-21 mantled by narrow zones of Wo6-10Fs10-16 plus metal; augite is Wo33-35Fs13-14; spinel contains 42-59% Cr2O3, 16-31% Al2O3, and <3% FeO. The spinels are surrounded by complex zones consisting of Cr-Fe metal, brezinaite (Cr-sulfide), and skeletal crystals of corundum-Cr2O3(-CrO?) solid solution (up to ~82% Al2O3, MgO <<1%) embedded in Na-Ca-bearing aluminosilicate glass. This meteorite is a highly unusual ureilite.
Oxygen Isotope Composition: Robert Clayton LEW88774,3 has δ18O = +7.62 per mil; δ17O +3.03 per mil. This composition falls within the field of ureilites of Group I of Berkley et al. (Geochim. Acta 44, 1579, 1980). The mean of 10 Group I meteorites is δ18O = +7.52 per mil, δ17O = +3.12 per mil (Clayton and Mayeda, Geochim. Acta 52, 1313, 1988).
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| Data from: MB76 Table 2 Line 4614: |
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| References: | Published in Antarctic Meteorite Newsletter 16(1) (1993), JSC, Houston Published in Meteoritical Bulletin, no. 76, Meteoritics 29, 100-143 (1994)
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Geography:
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Statistics: This is 1 of 43840 approved meteorites from Antarctica (plus 3802 unapproved names) | ||||||||||||||||||||||||
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