CR Carbonaceous Chondrites


Northwest Africa 1180

Morocco
Found 2000
Carbonaceous chondrite (CR2)

Eight fully to mostly crusted stones, weighing a total of 1705 g, were purchased in Rissani (2001). The local finders say that these stones defined a strewn field ~1.5 km long and within a few kilometers of Zagora. Classification and mineralogy (T. Bunch and J. Wittke, NAU): chondrules account for 63 vol. %; small chondrules (<1.5 mm) tend to be round and metal-poor, large chondrules (<4.0 mm) are mostly irregularly shaped with abundant metal (kamacite = 5.2-6.0 wt. % Ni). Olivine, Fa1.3-2.1; orthopyroxene Fs2.2-3.2Wo0.8; plagioclase, An95-97; pyrrhotite (Ni = 1.4 wt. %); phyllosilicates, serpentine-greenalite series (Mg > Fe); chondrule and matrix glasses are Mg-, Al-rich, Na-, K-poor; fine-grained (<0.05 mm) refractory inclusions contain diopside (Wo49-52Fs1), spinel (FeO = 0.25 wt. %), and gehlenite, Shock stage, S1; weathering grade, W2. Specimens: type specimen, 19.7 g and one thin section, NAU; main mass is with purchaser.

NWA 1180 © T. E. Bunch, 2004


Northwest Africa 3105

Morocco
Found 2001
Carbonaceous chondrite (CR2)

A single 89.2 g stone with 80 % crust was purchased in Rissani, Morocco in 2002. Description and classification (J. Wittke and T. Bunch, NAU): mostly even-sized (1-2 mm) chondrules are slightly flattened and define a preferred orientation. A few chondrules are completely rimmed by metal (Ni = 6.3 wt. %). The matrix contains numerous round metal grains (0.3 to 1.8 mm diameter) and smaller (< 0.4 mm), irregular metal with included olivine and pyroxenes. Rare CAI amoeboids and patches of phyllosilicates are sparsely distributed throughout the matrix. Matrix olivine, Fa1.4-6.6 and orthopyroxenes, Fs3.4–5.2 Wo0.3-0.7. Shock stage, S2; weathering grade W1. Specimens: 12.35 g, NAU; main mass, Oakes.

NWA 1180. Combined reflected/transmitted light image. White areas are metal. Note metal-rich rims around most of the large chondrules. © T. E. Bunch, 2004