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An MPOD Classic
from 3 August 2013

 
ALH 77003   contributed by AMN   MetBul Link
 


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780 grams.   CO3.6

Fall not observed. Found 1977 in Antarctica.

Location Map of Antarctic Falls

AMN writes:
Macroscopic Description
Specimen is very well rounded. No surface fissures are present. Fusion crust covers 33% of the meteorite’s surface, (~100% T surface, 30% N and W surfaces, and 10% of E surface) and ranges from 1 to 3 mm thick. The crust is medium black and slightly glassy. The fusion crust is preserved on the surface (s) that were uppermost at the time of discovery (see field photo). The remaining surface of the meteorite is smooth, brownish-black, and has little iron-oxide staining. This surface is polished and may be the lower part of a fusion crust or a wind-polished surface. In an area ~l cm x 2 cm this surface has been removed, revealing an interior surface that is partially iron-oxide stained. This is a well indurated specimen. Repeated attempts to chip this meteorite for thin section samples were all partially successful.
Thin Section Description (,2) - Brian Mason
Numerous and well-defined chondrules, 0.1-0.6 mm in diameter, along with mineral clasts are present in a fine-grained groundmass colored brown with limonitic material. The chondrules exhibit a variety of form and structure, the commonest consisting of granular aggregates of olivine and polysynthetically twinned clinopyroxene; some chondrules have pale brown transparent glass interstitial to the olivine and pyroxene grains. Microprobe analyses show that both olivine and pyroxene are highly variable in composition. Olivine ranges from Fa4 to Fa48 with a mean of Fa22; pyroxene ranges from Fs2 to Fs25, with a mean of Fs14, and its calcium content averages 1% CaO. The highly variable composition of olivine and pyroxene indicates a type 3 chondrite, and the mean composition of the olivine and small amount of nickel-iron suggest L group, so the meteorite is tentatively classified L3; however, certain assignment of group should await further investigation.
Reclassification Notes (31,1)
Reclassified as CO3.6 Chondrite in AMN 31,1. References: subtype classification, E.R.D.Scott and R.H.Jones, 1990, GCA 54, 2485; TL data, petrologic type 3.4, D.W.G.Sears et al., 1991, Proc. NIPR Symp. Ant. Met. 4, 319


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Bob Verish
 8/3/2018 2:31:59 PM
Reclassified in 1990 as CO3.6 -- BUT in 1991 as CO3.4 Why is the latter reclassification ignored?
John Divelbiss
 8/3/2018 9:17:08 AM
Interesting read for this find. It is a CO3.6 but was originally thought to be a L3. Secondly there is a note about how "hard" this meteorite is...where talking about the meteorite being a "well indurated" specimen when attempts to break/chip it were only partly successful.
 
 


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