Frontier Mountain 03022

Antarctica

Found 2003 December 29

Achondrite (polymict ureilite)

A stony fragment weighing 2.47 g was found by a PNRA team on the Frontier Mountain blue ice field. Mineralogy and classification (A. M. Fioretti and R. Carampin, Istituto di Geoscienze e Georisorse – CNR, Padova): polymict ureilite breccia containing a wide variety of mineral and lithic clasts <2 mm in size. Typical ureilite clasts show equilibrated texture with triple junctions, intergranular lamellae of graphite, and olivine cores ranging from Fo₇₅ to Fo₈₇ with highly reduced rims (up to Fo₉₃). Most isolated olivine crystals show the same compositional range. Low-Ca pyroxene in lithic clasts and isolated crystals shows a wide compositional range, En_67-99 Wo_0.2-12. Rare augite is found as isolated crystals. Individual plagioclase crystals are mainly albitic, Ab_94.7 Or_7.14. Interstitial glass has high SiO₂ content (up to 75 wt%).  The breccia contains five very fine-grained dark clasts, up to 1.8 mm in size, similar carbonaceous chondrite matrix material. The clasts are almost opaque and contain both Mg-rich and Fe-rich, very fine-grained hydrous minerals. Opaque mineral include abundant troilite and minor kamacite, schreibersite. Shock varies in the different up to shock stage S5. Weathering is minor, W1. Specimens, main mass MNA-SI.