Abstract
The Hammadah al Hamra 193 winonaite was found in the Libyan desert in 1996. Unlike most winonaites with fine- to medium-grained equigranular textures, it consists predominantly of very large (up to 5 mm), optically continuous orthopyroxene grains enclosing smaller grains of olivine and plagioclase. It also contains large (up to 2 mm) poikilitic grains of amphibole enclosing clinopyroxene, plagioclase, olivine, and occasionally orthopyroxene, which occur interstitial to the large orthopyroxene grains. The amphibole is identified as fluoro-edenite, and textures indicate that it replaces clinopyroxene via a reaction in which diopside, olivine, and plagioclase form fluoro-edenite. Trace-element data are consistent with the formation of fluoro-edenite from clinopyroxene and plagioclase. Fluoro-edenite has a REE pattern similar to that of clinopyroxene, but has elevated abundances of Na, K, and Ba, elements typically enriched in plagioclase. The source of the F is uncertain, but may be apatite, which is fluor-apatite in this meteorite. The presence of fluoro-edenite in HaH 193, a meteorite that experienced extensive thermal metamorphism, indicates a significant stability field for this rare mineral.
© 2015 by Walter de Gruyter Berlin/Boston
