Yucca 045        34°45.894’N, 114°14.101’W

Arizona, United States

Find: 27 Mar 2011

Classification: Ordinary chondrite (H3-6)

History: Found with metal detector 6 inches below the surface in the Yucca DCA by Jim Wooddell March 27, 2011. Entire stone donated to Cascadia.

Physical characteristics: Exterior is covered with weathered fusion crust, with large patches of reddish-brown rust.

Petrography: In thin section, two distinct lithologies that appear lighter and darker in plane-polarized light are visible and have irregular and gradational boundaries. The light lithology is coarser grained and contains chondrules with boundaries integrated into their surroundings. Feldspar is variable in size, most slightly below 50 µm in diameter, but with a few larger grains. The dark lithology is dominated by fragmental material containing numerous small cryptocrystalline chondrules; BSE imaging shows that this lithology 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). This lithology also contains occasional coarse feldspar grains (most below 50 µm in diameter), coarse phosphate grains, and numerous chromite-plagioclase assemblages. FeNi carbide with some accompanying magnetite, alumnious low-calcium and high-calcium pyroxenes, and silica polymorph are present in the dark lithology. Along two edges of the section abutting the dark lithology is a small patch of shock melt (opaque in plane-polarized light) containing metal and troilite blebs, and a coarse-grained clast lacking chondrules.

Geochemistry: (M. Hutson and A. Ruzicka, Cascadia) Light lithology olivine (Fa_19.6±0.6, N=7) and low-Ca pyroxene (Fs_17.6±0.9Wo_1.3±0.2, N=5) are consistent with a type 5 or 6 designation. Dark lithology olivine (Fa_17.7±9.2, N=35) and low-Ca pyroxene (Fs_15.4±6.5Wo_1.2±1.0, N= 33) compositions reflect the large admixture of type 3 material. Fragments in this lithology include a partial chondrule containing dusty forsteritic olivine grains (Fa_0.7±4.0) and aluminum-rich diopside (6 wt% Al₂O₃) set in anorthitic glass (An₉₂Or₀), as well as a fragment of a ferroan chondrule with olivine (Fa_34-51) and low-Ca pyroxene (Fs₂₄ Wo₅) set in a Na-K-rich glass. The coarse-grained clast at the edge of the section consists of equilibrated olivine (Fa_19.3±0.3, N=10), low-Ca pyroxene (Fs_16.9±0.2Wo_1.5±0.4, N=9), and feldspar (Ab_78.2±1.4An_14.4±0.7Or_7.4±0.8, N=2).

Classification: H3-6 finely intermixed genomict breccia. Light lithology is type 5-6 material as implied by medium to coarse feldspar grain sizes and equilibrated olivine and pyroxene; dark lithology contains type 3 material as implied by common presence of magnesian and zoned olivine. Paired with Buck Mountain Wash (synonymous with Yucca 002) on the basis of mineralogy, mineral chemistry, and texture.

Specimens: Cascadia holds 38.0 g in two pieces, in addition to one polished thin section and a mounted butt.