Yucca 048        34°49.402’N, 114°16.573’W

Arizona, United States

Find: 23 Sep 2012

Classification: Ordinary chondrite (H3-6)

History: Found with metal detector in the Yucca DCA by Troy Ball September 12, 2012. 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 with only 8 complete chondrules visible; 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 a large coarse-grained clast with anhedral olivine grains up to 1mm across, a shock melt clast with zoned olivine grains set in a ferromagnesian glass, and a small (~70 µm across) chondrule that contains numerous spinel grains [(Mg0.7Fe0.3)Al2O4] and ilmenite set in a Ca, Mg, Al-rich glass and surrounded by a shell of Al-rich low-Ca pyroxene. Abundant FeNi carbide with some accompanying magnetite is found only in the dark lithology.

Geochemistry: (M. Hutson and A. Ruzicka, Cascadia) Light lithology olivine (Fa_19.3±0.8. N=8) and low-Ca pyroxene (Fs_16.8±0.7Wo_1.7±0.8) are consistent with a type 5 or 6 designation. Dark lithology olivine (Fa_17.6±9.6, N=22) and low-Ca pyroxene (Fs_13.9±4.8Wo_1.4±0.7, N= 30) compositions reflect the large admixture of type 3 material. The coarse-grained clast in the dark lithology consists of highly equilibrated olivine (Fa_19.0±0.1, N=8), low-Ca pyroxene (Fs_16.7±0.1Wo_1.4±0.1, N=5), diopside (Fs_5.4±0.3Wo_47.3±0.2, N=5), and feldspar (Ab_70.7±3.5An_24.2±4.5Or_5.1±1.4, N=8).

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 (dark lithology). Paired with Buck Mountain Wash (synonymous with Yucca 002) on the basis of mineralogy, mineral chemistry, and texture.

Specimens: Cascadia holds 19.3 g in multiple pieces, in addition to one polished thin section and a mounted butt.