Northwest Africa 13791 (NWA 13791) Purchased: 2020 Classification: Ungrouped achondrite Petrography: (K. Metzler, IfP) Equigranular igneous rock with some vesicles. It consists of ~85% mafic components (olivine and low-Ca pyroxene with Ca-rich pyroxene rims) and ~15 vol% fine-grained interstitial material. The typical grain size is ~300-1000 µm. Metal and sulfide beads up to 800 µm are completely oxidized by terrestrial weathering. Geochemistry: Mineral compositions and geochemistry: Olivine grains show igneous chemical zoning, with increasing Fe concentrations from core to rim. Mean olivine composition is Fa20.5±3.2 (Fa16.4-29.5; n=17); Fe/Mn (at.): 50±12. Mean low-Ca pyroxene composition is Fs20.1±0.9Wo2.7±0.3 (Fs18.1-21.4Wo2.2-3.1; n=17); Fe/Mn (at.): 29±10. The mean composition of Ca-rich pyroxene is Fs18.6±2.1Wo28.1±3.9 (Fs15.0-22.3Wo21.7-34.1; n=8); Fe/Mn (at.): 28±7. Mean bulk composition of fine-grained interstitial material (EDX analyses; area ~50x100 µm; wt%): SiO2 64.2; Al2O3 17.1; Na2O 9.4; FeO 4.2; CaO 3.2; MgO 0.5; K2O 0.8; TiO2 0.7. Based on mineral chemistry, this sample has affinities to L or H ordinary chondrites. Classification: Ungrouped achondrite: The combination of mineral compositions does not fit to any known achondrite group, although it exhibits affinities to H or L ordinary chondrites. Shock stage: M-S1 Weathering grade: high Classifier: K. Metzler, IfP This lot comes with certificate of authenticity. Thanks for your interest.