Winona meteorite, Winona, Coconino County, Arizona, USAi

Regional Level Types
Winona meteorite	Meteorite Fall Location
Winona	Town
Coconino County	County
Arizona	State
USA	Country

A meteorite found 0.9 km (0.6 mile) SE of Winona.

Winonaite Prototype (primitive achondrite)
1928 find, weathered; shock level, mild (S1), 24 kg

A weathered mass was removed from a burial cyst in the ruins of the Elden Pueblo. The mass broke into fragments upon removal as its metallic iron and several other iron-rich minerals had been largely weathered way. In time, however, this rather curious reduced assemblage — rich in equigranular enstatite-rich pyroxene (Fs6) and forsteritic olivine (Fa5) accompanied by metallic iron and troilite — was seen to be a template for a new meteorite geochemical group, the Winonaites. This relatively small group of meteorites is roughly chondritic in composition with reduced silicate compositions very similar to that of the Kakangari-like (K) chondrite group. As of early June 2014, 25 have been listed on the Meteoritical Society's Home page — but this list includes several possible paired Northwest Africa stones. Even though a few relic chondrules have apparently been found in a few Winonaites, they are classified as achondrites because their dominant texture is that of melted rock. Their oxygen isotope ratios and other characteristics also indicate a close relationship to the IAB irons with silicate inclusions. While ten Winonaites are known with masses greater than 100 grams, Winona is by far the most massive. This is true even though Winona has apparently lost a significant fraction of its mass to weathering processes. A single, small Winonaite fall (Pontlyfni) is known. However, Winona had already been established as a fiduciary reference point ('prototype') before Pontlyfni's geochemical and mineralogical similarities to Winona were widely recognized. [Winona is one of the few meteorite prototypes whose fall was not observed].

Winona constituents are, roughly, 50 vol% Orthopyroxene (Fs ~6), 15 vol% Olivine, ~10 vol%, Plagioclase, plus ~25 vol% opaques and other minor phases (Cf. Floss et al., 2008). Within the meteorite are coarse-grained lithologies & finer-grained lithologies whose varying mineral proportions may account for some difference abundances in the cited references. Fe-Ni iron and troilite are still found in residual veins, but determining the original amounts of Fe-Ni iron and troilite from the residues and weathering products makes any quantitative estimate of the original mineralogy somewhat problematic. However, the presence of accessory amounts of alabandite, apatite, chromite, clinopyroxene, daubréelite, diopside, graphite and schreibersite is quite informative. These minerals — often rare or even unknown in terrestrial rocks — also indicate that the Winona meteorite indeed came from a very reducing environment. Among stony meteorites, more reducing mineralogical assemblages have usually been found only among the Enstatite Chondrites and Enstatite Achondrites. The Winona meteorite is indeed a useful prototype for this group of primitive achondrites. However, in this case it is especially important to complement our inquiries with additional information provided by the smaller, less weathered Winonaites.

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