Northwest Africa 8534 (NWA 8534)

(Northwest Africa)

Purchased: 2014 Jun 12

Classification: Carbonaceous chondrite (CM1/2)

History: Purchased 12 June 2014 in Morocco.

Physical characteristics: Many identically appearing small fragments, the largest being 2.6 g, with black, fresh fusion crust. Broken surface reveals black, uniform, very fine-grained texture, rare sub-mm CAIs, with no visible chondrules.

Petrography: (C. Agee, UNM) Microprobe examination of a polished mount shows a matrix (80-90%) dominated by (Mg,Fe)-rich phyllosilicates, with scattered, small (~250 μm), mostly irregularly shaped chondrules, many of which contain secondary alteration phases. There is no mesostasis in any chondrule; they are all altered. This meteorite is transitional between CM1 and CM2. There is more fine-grained (80-90%, dominantly phyllosilicate) matrix than in CM2, but less than CM1. Calcium carbonate, (Ca,Mg)-carbonate, sulfides, and Fe-oxides are ubiquitous.

Geochemistry: (C. Agee and N. Muttik, UNM) Ferroan olivine Fa_25.3±23.9, Fe/Mn=78±39, Cr₂O₃=0.40±0.09 (wt%), n=4; forsterite Fa_1.4±0.4, Fe/Mn=15±14, n=16; aluminous diopside Fs_2.9±1.6Wo_47.4±9.6, n=3. Oxygen isotopes (K. Ziegler, UNM): acid-washed material analyzed in 8 replicates by laser fluorination gave, respectively δ¹⁸O=10.694, 15.433, 9.721, 12.571, 12.343, 13.254, 12.798, 12.440; δ¹⁷O=3.496, 6.442, 2.651, 4.363, 4.207, 4.863, 4.722, 4.450; Δ¹⁷O= -2.150, -1.706, -2.481, -2.274,-2.310, -2.135, -2.035, -2.118 (all per mil).

Classification: Carbonaceous chondrite (CM1/2), the petrologic type 1/2 is based on the relatively low abundance of chondrules and refractory inclusions, the high abundance of hydrous phases, and high volume percentage of matrix. It is also based on the mean value of eight oxygen isotope analyses that plots outside the field of CM2, at higher values δ¹⁷O=4.399±1.096 and δ¹⁸O=12.407±1.699 permil.

Specimens: 12 g including a probe mount on deposit at UNM, Robert Cucchiara and Ruben Garcia hold 48 g.