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Lewis Cliff 88774
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:help 3.1 g
Classification
  history:
Antarctic Meteorite Newsletter:  AMN 16(1)  (1993)  Ureilite
AMN 17(1)  (1994)  Ureilite-an
Meteoritical Bulletin:  MB 76  (1994)  Ureilite-an
NHM Catalogue:  5th Edition  (2000)  Ureilite-an
MetBase:  v. 7.1  (2006)  Ureilite-an
Recommended:  Ureilite-an    [explanation]

This is 1 of 6 approved meteorites classified as Ureilite-an.   [show all]
Search for other: Achondrites, Ureilites
Comments: Field number: 5323
Writeuphelp
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).

 

Data from:
  MB76
  Table 2
  Line 4614:
Origin or pseudonym:Lower Ice Tongue
Mass (g):3.1
Class:Ur an
Weathering grade:B/C
Fayalite (mol%):25
Ferrosilite (mol%):10-21
Plots: O isotopes:  
Catalogs:
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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:

Antarctica
Coordinates:
     Catalogue of Meteorites:   (84° 17'S, 161° 5'E)
     Recommended::   (84° 15' 2"S, 161° 27' 33"E)
Note: the NHM and MetBase coordinates are 5.6 km apart

Statistics:
     This is 1 of 41908 approved meteorites from Antarctica (plus 3802 unapproved names)
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