The basaltic shergottite Northwest Africa 856: Petrology and chemistry

We report on the discovery of a new shergottite from South Morocco. This single stone weighing 320 g is referenced as Northwest Africa (NWA) 856 with Djel Ibone as a synonymous name. It is a fresh, fine-grained basaltic rock consisting mainly of two pyroxenes (total similar to68 vol%: 45% pigeonite, En(61-16)Wo(9-22)Fs(26-68); 23% augite, En(46-26)Wo(34-29)Fs(21-43)) and plagioclase converted to maskelynite (similar to23 vol%, Ab(43-57)Or(1-5)An(54-36)). Accessory minerals include merrillite, Cl-apatite, pyrrhotite, ilmenite, ulvospinel, silica (stishovite and glass), amorphous K-feldspar and baddeleyite. Amorphous mixtures of maskelynite and silica occur most commonly as median layers inside maskelynite laths. In addition, melt pockets (similar to2 vol%) were recognized with relics of maskelynite, pyroxene and both dense silica glass and stishovite occurring as both grains and submicrometer needles. The compositions of the melt pockets are consistent with mixtures of maskelynite and pyroxenes with an average of similar to50 vol% maskelynite. The meteorite is highly fractured at all scales.

Published in:
Meteoritics & Planetary Science, 37, 1147-1164

 Record created 2011-09-29, last modified 2018-01-28

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