Hammadah al Hamra 193: the first
amphibole-bearing winonaite
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 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 fluorine 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.
Floss et al. (2007) Am. Mineral. 92, 460-467.
Full publication: 2007_AM92_460.pdf
Last revised: 4-2007