Antarctic Search for Meteorites (ANSMET) Search this
Place:
Antarctica
Collection Date:
1988
Notes:
# NASA data for LEW 88774 Weathering: B/C Fracturing: A Fa: 25 mol % Fs: 10-21 mol %
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.
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.<br />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.<br />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.
