Enstatite Achondrites


Northwest Africa 1840

Morocco
Found 2003
Enstatite achondrite

A 132.8 g complete and partially crusted stone was purchased in Erfoud, Morocco in August 2003. Description and classification (T. Bunch and J. Wittke, NAU): The meteorite has an igneous texture; it is a brecciated enstatite orthopyroxenite with a series of prominent, parallel compression fractures (0.1 to 0.8 mm spacing) that span the entire sample. These fractures acted as conduits for weathering; most weathering effects are limited to areas that border these fractures. Mineral modes: enstatite, 92 vol. %; Si-bearing metal, 4 %; plagioclase (maskelynite), 2 %; high Cr-troilite, 2 %; graphite, < 1%. Enstatite, FeO = 0.03 to 0.64 wt. %; CaO = 0.06 to 0.38 wt %.; Cr-rich troilite, Cr = 10.2 to 14.7 wt. % with Mn < 1.15 % and Ti < 1.76 wt. %. Largest metal grains (0.6-1.0 mm dia.) have graphite inclusions < 0.1 mm in size; metal, Ni = 6.5 wt. % (range = 6.2-6.9), Si = 1.25 wt. % (range = 0.9-1.81); plagioclase, An42. None of the exotic sulfides common to aubrites and enstatite chondrites were found. Shock level, S4 (parallel fractures, reduced birefringence, and mottled extinction in enstatite; all plagioclase is maskelynite); weathering grade is W2/3. Specimens: type sample, 21.1 g (NAU); main mass, Oakes.

NWA 1840 © T. E. Bunch, 2004

NWA 1840 © T. E. Bunch, 2004