Northwest Africa 720 (NWA 720)

Morocco

Purchased: 2001

Classification: Ordinary chondrite (LL6)

History: Sample origin Boudnib, purchased Alnif in Jan 2001. Provisional 23.1 g sample at UCLA. Type sample is catalogued at the ROM as M52971.

Physical characteristics: Blocky individual with two generations of fusion crust, ranging from smooth curved to sub-cm regmalypted, implying that this stone is a fragment from a larger fall. Broken surfaces (40%) and fusion crust surfaces show mature desert polish. Physical properties: Magnetic susceptibilty of a 2.18 g specimen is log χ (× 10^-9 m³/kg) = 4.03.

Petrography: Cut face (10 cm2) shows a green stone with dark, irregular cm wide veins of fine grained material. Metal is sparse, with associated local Fe oxides. Dark veins have associated Fe oxide staining but are generally devoid of visible metal grains. In polished thin section, chondrules are poorly delineated in a coarsely recrystallized matrix. A representative dark 8 mm wide vein cuts the chondrite with sharp contacts and contains fragments of large chondrules, lithic chondritic clasts and finer chondritic debris. Metal grains up to 400 µm in the host chondrite show embayed texture on silicates; metal grains are much smaller in the dark vein. Sulfides are abundant and finely disseminated in both chondritic host and vein. Shock veins up to 30 µm width partly defined by sulfide fill cross cut and offset the chondritic host and dark vein material. Olivine and pyroxene typically show undulatory to mosaic extinction.

Classification: Ordinary chondrite LL6 (S4) W2. Low observed metal content and magnetic susceptibility are consistent with LL chondrite. Stone appears to be an LL6 breccia with dark veins of fragmental material that subsequently developed shock veins.

Specimens: Type specimen ROM; main mass Gregory