Hammadah al Hamra 317

Libya

Found 2001 spring

Enstatite chondrite (EL4)

Two dark brown stones, a larger one of 103 g and a smaller one of 2 g were found in the Hammadah al Hamra region. Classification and mineralogy (G. Pratesi, V. Moggi Cecchi, MSP): the partly fusion-crusted stone is shield-shaped; well­defined chondrules and 50 µm sized enstatite crystals indicate petrologic type 4. Major phases are enstatite (En98.5Wo0.9), kamacite (Fe = 90.46, Ni = 7.51, Si = 0.57, P = 0.53, Co = 0.47 wt%) and troilite; other minor phases are diopside(En52.91Wo46.85) and plagioclase (An26.60) in very small grains (<5 µm). Neither niningerite nor alabandite was found. The plagioclase composition, as well as the presence of diopside, is unusual compared with other known EL chondrites. Inside the chondrules, which have an average size ranging from 600 to 1200 µm, very small rounded grains containing a calcium chloride phase (1–3 µm size) have been observed. Based on texture, mineralogy and chemistry (mainly An content of plagioclase >13 mol% and Si content of kamacite <1.9 wt%; Keil, 1968; Zhang et al., 1995) the meteorite is classified as an EL4 chondrite. Terrestrial weathering grade is rather low (W1); optical features (undulatory extinction of enstatite) indicate that the sample is weakly shocked (S3). Specimens: main mass, type specimen and thin section, MSP.