Allan Hills A77230 meteorite, Allan Hills, Victoria Land, Eastern Antarctica, Antarcticai

Regional Level Types
Allan Hills A77230 meteorite	Meteorite Fall Location
Allan Hills	Group of Hills
Victoria Land	Region
Eastern Antarctica	Region
Antarctica	Continent

Ordinary Chondrite (L4; S2; W4)
Find,1977; 2.4773 kg

Allan Hills A77230 (ALHA77230) was a nearly complete moderate-sized, weathered meteoritic stone recovered by the joint US-Japanese Antarctic Meteorite program. In thin sections distinct chondrules and chondrule fragments are tightly packed within a medium-grained matrix. Olivine and pyroxene chondrules (mean diameters 0.3-2.0 mm) are present with barred and porphyritic olivine (BO,PO) and radial pyroxene (RP) chondrule types the most prominent. Two populations of chondrules can be distinguished — prominent spherical chondrules with a glassy mesostasis and other less defined chondrules partially integrated with the surrounding matrix. Average composition of olivine (Fa23) [and pyroxene (Fs~18)] is indicative of the L chondrite group. Partial integration of chondrules and matrix and the mild disequilibrium of olivine (Fa22-25) and the more marked disequilibrium of pyroxene disequilibrium (Fs18–29) account for the L4 petrologic type designation. Formal definition of L4 chondrites would normally indicate an absence of primary glass. In this instance, apparently, the petrologic type 4 designation represents a characterization of the overall status for what is an oddly heterogeneous aggregate. Troilite and lesser amounts of Fe-Ni metal appear in pooled, interstitial metal-troilite aggregates. Weathering grade (W4) is based upon the presence of significant rust in fissures and limonite staining.

A few studies have been published which have been more focused on reconstructing the thermal history of ALHA77230 (along with other chondrites) rather than reporting on its mineralogy per se. A somewhat tentative K-Ar age of ~3.4 Ga suggests that ALHA77230 has experienced at least one major disruption since it original aggregation and, presumably, before it was ejected into an earth-crossing orbit.

References

External Links

Other Regions, Features and Areas containing this locality