Moapa Valley                      36°33′26"N, 114°25′37"W

Clark County, Nevada, United States

Find: September 2004

Carbonaceous chondrite (CM1)

History: The specimen was found by Sonny Clary in September, 2004, in the Moapa Valley, southeast of Logandale, Nevada.

Physical characteristics: A single dark gray, flattened stone (698.8 g), exhibiting subparallel contraction cracks and partially coated with black, vesicular fusion crust.

Petrography (A. Irving and S. Kuehner, UWS): Rounded to ellipsoidal objects (0.05 to 0.7 mm across), exhibiting a preferred orientation of their long axes, are set in a fine-grained, dark matrix containing small clusters of sulfide grains. The larger objects are composed mainly of serpentine minerals and S-bearing phase(s) (probably tochinilite), and in thin section range in color from pale yellow-brown to reddish brown to sepia brown; some such objects have serpentine-rich rims and/or larger, subhedral, dark brown grains composed of serpentine/cronstedtite. Sulfides consist of finely intergrown pyrrhotite and pentlandite. Rare magnetite and calcite are present in the matrix, and the specimen is traversed by narrow open fractures and thin veinlets filled with chalcedony.

Geochemistry: Broad-beam EMP analysis of different components gave the following compositions (in wt%): ellipsoidal objects SiO₂ 31.7–38.4, TiO₂ 0.07–0.25, Al₂O₃ 1.8–7.2, Cr₂O₃ 0.19–0.73, FeO 15.9–26.3, MnO 0.07–0.18, MgO 22.7–28.8, CaO 0.06–0.25, Na₂O 0.04–0.29, SO₃ 0.03–0.87, sum 85.7–87.4; matrix SiO₂ 27.1–28.4, TiO₂ 0.11–0.16, Al₂O₃ 2.7, Cr₂O₃ 0.48–0.57, FeO 34.1–39.7, MnO 0.20–0.25, MgO 14.7–16.5, CaO 0.36–2.9, Na₂O 0.21–0.42, SO₃ 3.9–8.5, sum 89.9–94.1.

Oxygen isotopes (D. Rumble, CIW): analyses of two acid-washed whole rock fragments by laser fluorination gave, respectively, δ¹⁸O = 6.29, 6.08‰; δ¹⁷O = 0.93, 0.68‰; Δ¹⁷O = −2.382, −2.519‰.

Classification: Carbonaceous chondrite (CM1). The degree of terrestrial weathering is low.

Specimens: A total of 21 g, one polished thin section and one polished mount are on deposit at UWS. Mr. S. Clary holds the main mass.