Mineral chemistry of the shergottites, nakhlites, Chassigny, Brachina, pallasites and urelites

The mineral chemistry is compared for selected achondrites. Olivine in the ALHA 77005 and EETA 79001 shergottites, olivine-rich Chassigny and Brachina, and the nakhlites, contains Ni indicative of oxidizing conditions, whereas pallasitic and ureilitic olivines contain much lower Ni due to reducing conditions. The Brachina olivine and pyroxene have distinctively higher Fe/Mn than the shergottites and Chassigny, further indicating that Brachina is unique. The Chassigny and 77005 olivines contain lower Cr2O3 (0.03 wt. pct) than the Brachina and 79001 olivines. Values of Fe/Mn for cumulus augites in nakhlites are higher than for the shergottites, whereas those for ferropigeonites are not. The 77005 shergottite contains troilite FeS in contrast to 79001, Shergotty, Zagami, and Chassigny, which contain pyrrhotite. Further analyses are needed, but the present survey indicates that at least Brachina is not chemically cogenetic with the other 'oxidized achondrites', and that the Fe/Mn ratio of the cumulus augites in nakhlites is a problem for the assignment of the nakhlites, shergottites, and Chassigny to a single genetic group.