The Famenin fall and other ordinary chondrites intermediate between H and L groups

The Famenin meteorite fell around 08:30 a.m. local time (GMT+4.5) on June 27, 2015 on the roof of a house in Famenin, a town in NW Iran. A single 640 g stone was recovered, shattered into several pieces upon impact. The shape of the impact hole and the relative position of the recovered meteorites indicate a N-NW fall direction. Famenin is an ordinary chondrite (OC) with well-preserved chondrules of various types, (Fe,Ni) metal, troilite, phosphate, and chromite. The organic matter systematics and the olivine and low-Ca compositional distributions (percent mean deviations 18% and 31%, respectively) indicate it is a type 3.4/3.8 chondrite. Considering the average chemical compositions of olivine (Fa(17.5 +/- 4.7)) and low-Ca pyroxene (Fs(16.8 +/- 7.5)), average Co content of the kamacite (5.6 mg g(-1)), and Cu/Ni and Ga/Ni ratios, Famenin should be classified as an H chondrite. However, saturation magnetization is 26.0 Am-2 kg(-1), indicating a bulk metal content similar to L chondrites. Similarly, the whole-rock Ni and Co contents (13073 and 540 mu g g(-1), respectively), and average chondrule diameter (550 mu m) are closer to typical values for L chondrites than H chondrites. The (Fe,Ni) metal modal abundance (5 vol%), magnetic susceptibility, and possibly whole-rock oxygen isotopic composition indicate intermediate properties between H and L chondrites. Noble gas composition and cosmic-ray exposure ages of Famenin and El Medano 195 (another intermediate OC) shows their gas-rich character and an older ejection age from their parent body than those for the majority of H and L chondrites. Famenin, together with similar intermediate OCs, increases the diversity of this meteorite clan and suggests the existence of a separate OC group with a composition broadly intermediate between H and L groups for which a different designation (HL) is proposed. OCs likely originate from more than three parent bodies (H, L, and LL) as traditionally proposed.

Automated summary

The text discusses the discovery and characteristics of the Famenin meteorite in Famenin, Iran in 2015, as well as its chemical composition, origin, and classification. It suggests that Famenin is an intermediate type of ordinary chondrite with features between H and L chondrites, leading to the proposal of a new designation, HL group, to accommodate such meteorites.