Arivaca                       31° 35’ 38.09’’N, 111° 22’ 12.84’’ W

Arizona

Find: January 1999

Achondrite (eucrite)

History: Found by Carl Esparza on the historic Wilbur Cruce Ranch near Arivaca, Arizona, in January 1999.

Physical characteristics: A single 30.1 g naturally broken stone, about half coated by dark brown fusion crust. The weathered former interior surfaces are gray and white in color. Sparse small grains of metal are visible on a freshly cut surface.

Petrography: (A. Irving and S. Kuehner, UWS) The specimen is a breccia composed of fragments of ophitic-textured basaltic eucrites and related mineral fragments (possibly from more than one precursor lithology) plus small grains of Ni-poor metal. The major minerals are low-Ca pyroxene (mostly orthopyroxene with sparse exsolved blades of clinopyroxene, but also some homogeneous pigeonite) and calcic plagioclase, with accessory clinopyroxene, silica polymorph, ilmenite, chromite, and troilite (some finely intergrown with clinopyroxene and silica). Orthopyroxene host (Fs_55.3–55.7Wo_2.6–2.9, FeO/MnO = 30.5–34.6), plagioclase (An_82.5–83.7Or_2.1–1.9)

Classification: Achondrite (basaltic eucrite). This brecciated specimen contains more metal than most eucrites. Specimens: A total of 6.4 g and one polished thin section are on deposit at UWS. The main mass is held by CEsparza.