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Hammadah al Hamra 193: The first
amphibole-bearing winonaite.
Floss C., Jolliff B. L., Benedix G. K., Stadermann F. J.,
and Reid J. (2007)
Amer. Mineralogist 92, 460-467.
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 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.
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