Yucca 052        34°45.800’N, 114°14.349’W

Arizona, United States

Find: 27 Mar 2011

Classification: Ordinary chondrite (H3-5)

History: Found with metal detector by Jim Wooddell, March 27, 2011. Cut in 3 pieces. Jim Wooddell retained 1.2 gram slice, with remainder donated to Cascadia.

Physical characteristics: Exterior is covered with weathered brown fusion crust.

Petrography: In plane-polarized light, the thin section consists of a main lithology composed mainly of chondrule fragments, two light and two dark clasts, and a clast with a well-defined boundary that contains delineated chondrules in a dark matrix. BSE imaging of the main lithology shows that it contains a mix of equilibrated silicates, with a fairly large (~25-35 area %) admixture of type 3 material (both magnesian and iron-rich olivine and pyroxene grains). Feldspathic material is mainly glass, although small (less than 20 µm in diameter) feldspar grains are present. This lithology includes grains of silica polymorph, FeNi carbide, aluminous high-Ca pyroxene, chlor-apatite and merrillite. One large chondrule fragment shows signs of aqueous alteration before it was incorporated into the main lithology. This fragment consists of olivine grains that have irregular Fe-rich rims set in a pyroxene-normative glass that has rims and cross-cutting veins of Fe-rich glass. One of the two dark clasts is along the edge of the section and is dark due to the presence of an extensive web of weathering veins. The other dark clast is shock-blackened and contains numerous parallel veins of partially weathered metal and troilite. BSE imaging of the two light clasts shows that they consist of equilibrated silicates. Minerals present include phosphate grains, including a single large (> 300 µm across) grain of merrilite, plagioclase feldspar (less than 20 µm in diameter), and chromite-plagioclase assemblages. BSE imaging of the clast with well-defined chondrules shows that it consists of unequilibrated chondrules (rather than fragments) set in an Fe-rich, fine-grained matrix typical of a type 3 chondrite (hereafter referred to as the type 3 clast).

Geochemistry: (M. Hutson and A. Ruzicka, Cascadia) Light clast olivine (Fa_18.9±1.6, N=14) and low-Ca pyroxene (Fs_17.4±1.0Wo_1.1±0.7, N=10) are consistent with an H chondrite of petrographic type 5. The dark clasts were not analyzed. The main lithology has olivine (Fa_17.0±6.1, N=47) and low-Ca pyroxene (Fs_15.4±5.0Wo_1.4±0.9, N= 56) compositions suggestive of petrographic type 3, but petrographically resembles the "main lithology" of Buck Mountain Wash, which is a fragmental mixture of equilibrated and type 3 material. The type 3 clast has olivine (Fa_18.3±8.1, N=44) and low-Ca pyroxene (Fs_11.5±8.1Wo_1.1±1.1, N=35) compositions consistent with a type 3 designation. The large chondrule fragment which appears to have been aqueously altered has olivine grains with cores of Fa_16.3±2.3, N=10, consistent with an H-group precursor. The irregular rims on these grains are Fa_43.4±3.4, N=7.

Classification: H3-5 genomict breccia. Paired with Buck Mountain Wash (synonymous with Yucca 002) on the basis of mineralogy, mineral chemistry, and texture.

Specimens: Cascadia holds 19.8 g in two pieces, in addition to one polished thin section and a mounted butt. Jim Wooddell holds a 1.2 g slice.