Winonaites
Name
*click on the Name for more information
Structure Class
Primitive achondrites
Chemical Class
Winonaite
Country
Year found
unknown
Mass
3.82 kg
[Museum Collection]
(1) 89.10g
(E. Jacquet, MNHNP) NWA 725 was originally classified as an acapulcoite on the basis of its reduced mineral chemistry (Fa6.1, Fs7.5). However, O isotope measurements of Greenwood et al. (2012) (see e.g. their Fig. 9) plot in the field of winonaites. The mineral chemistry, by itself, was ambiguous (i.e. lying in the overlap between acapulcoites and winonaites) as recognized by Keil and McCoy (2018) (see their Fig. 4), who excluded NWA 725 from their review of acapulcoites and lodranites. Becayse there seems to be a consensus on the matter (e.g. Zeng et al. 2019), NWA 725 should be reclassified as a winonaite (and an interestingly chondritic one at that).
Name
*click on the Name for more information
Structure Class
Primitive achondrites
Chemical Class
Winonaite
Country
(Northwest Africa)
Year found
2019
Mass
8.03 kg
[Museum Collection]
(1) 9.9g (2) 9.7g
History: Three stones of similar size were purchased by Dr. Albert Jambon in August 2019 from a dealer in Nouakchott, Mauritania. Physical characteristics: About 80% of the surface of each stone is wind ablated with prominent metal veins and wedges separating depressed silicate regions, but remnant regmaglypts can be discerned. Large exposed metal areas exhibit a visible Widmanstätten pattern as thin, shiny taenite bands separating millimetric kamacite with a greenish oxidized surface. The bottom (formerly buried) sides of the stones are covered with remnants of weathered fusion crust. Fine grained olivine and green pyroxene are observed in places where the crust is missing. Petrography: (A. Irving, UWS and P. Carpenter, WUSL) Silicate-rich regions of the specimen have a metamorphic, triple grain junction texture (mean grainsize ~150 µm) and are composed of olivine, orthopyroxene, sodic plagioclase, kamacite, taenite and troilite. Cross-cutting metal-rich veins and patches are composed predominantly of kamacite and taenite. Geochemistry: Olivine (Fa1.1-1.3, FeO/MnO = 3-5, N = 5), orthopyroxene (Fs6.5-6.9Wo1.8-2.1, FeO/MnO = 9-10, N = 4), plagioclase (An14.8-15.4Or3.1-3.4, N = 2). Oxygen isotopes (K. Ziegler, UNM): analyses of acid-washed subsamples by laser fluorination gave, respectively, δ17O 1.969, 2.049, 2.119; δ18O 4.730, 4.887, 5.035; Δ17O -0.528, -0.531, -0.540 per mil. Classification: Winonaite (metal-veined). Specimens: 33.3 g including one polished thin section at UWB; remainder with Dr. A. Jambon.