Northwest Africa 10929 (NWA 10929)

(Northwest Africa)

Purchased: 2015

Classification: HED achondrite (Diogenite)

History: On 2015, meteorite specimens were purchased by José Antonio Sanchez Santana in the Saharawi refugee camps in Tindouf, Algeria.

Physical characteristics: Three stone fragments (34, 23 and 3 g) with black fusion crust covering 10% of the stones. A saw cut and broken surface reveals numerous mm-sized green crystals set in light-yellow groundmass.

Petrography: Petrographic description (J. Llorca, UPC). The meteorite is a orthopyroxene-rich breccia dominated by <1 to 4 mm grains set in a fine-grained cataclastic orthopyroxene matrix. The section contains about 99 vol.% orthopyroxene with accessory kamacite (50-400 ?m), troilite (30-50 ?m), Al-rich chromite (10-50 ?m) and Ca-rich pyroxene (50-100 ?m). Most accessory minerals surround large orthopyroxene grains. The section is notable for the absence of olivine and plagioclase.

Geochemistry: Mineral compositions (R.P. Lozano, IGME). Large grains and matrix unzoned orthopyroxene have the same compositions. Microprobe analyses show orthopyroxene ranges from Fs_25-30Wo_1-2 with a mean of Fs_26.4±1.2Wo_1.7±0.2 and Fe/Mn=35-47 (mean Fe/Mn=40.3±3.7) (n=17). Ca-rich pyroxene ranges are Fs_9-11Wo_44-46 (means: Fs_9.4±1.0Wo_44.5±0.8) and Fe/Mn=24-75 (mean: Fe/Mn=39.5±19.4) (n=6). The metal is kamacite whit Ni=1.3-1.5 and Co=1.1-1.2 (all in wt.%; n=16). Chromite has mean Cr/(Cr+Al)=0.93 (n=3). Bulk chemistry (J. Reyes, IGME). 0.5 grams of sample for analysis. XRF of subsample gave abundances of (in wt.%): SiO₂=53.56, TiO₂<0.10, Al₂O₃=0.52, Fe₂O₃=17.04, MgO=26.09, CaO=1.16 and K₂O<0.10. Na₂O= 0.05 wt.% by AAS. Trace elements were measured with ICP-MS (all in ppm): Be<0.1, V=85.3, Cr=2960, Co=10.7, Ni=13.9, Cu<0.5, Zn<2, As=0.14, Se<1, Mo<0.5, Ag<0.1, Cd=3.2, Sb=0.15, Ba=12.3, Tl<0.1, Pb<2, Th<0.1 and U<0.1.

Classification (R. P. Lozano, IGME). Achondrite, diogenite. Terrestrial weathering is not significant.

Specimens: Type specimen (11 g), two co-type specimens (1.0 + 2.1 g) and a probe mount are on deposit at Museo Geominero (IGME). A thin section is on deposit at UPC. José Antonio Sánchez Santana holds the main mass.