La’gad 002        27°14’25.7"N, 8°50’49.5"W

Saguia el Hamra, Western Sahara

Find: 2004

Classification: Pallasite (Main group, anomalous)

History: Near the end of 2004, Michael Farmer visited a site at the northeastern corner of Western Sahara in search of a newly discovered pallasite - www.meteoriteguy.com/catalog/almahbas.htm. This site yielded several large masses of a deeply weathered pallasite. In addition, Mr. Farmer collected and acquired several small fresh looking pallasite stones from the same site. The relationship between the large weathered masses and fresh stones is unknown. This pallasite is sold and traded under the name "Al Mahbas". The total mass of the weathered material is in the many kg range, whereas only a few grams, probably <100 g of the fresh stones was collected. ASU acquired one of the fresh stones upon which this classification is based.

Physical characteristics: Dark rounded stone with olivine grains visible at the surface.

Petrography: Cut, polished, and etched surface shows the following minerals (areal%) 70% metal, 20% olivine, and 5% troilite and schreibersite. Olivine grains are small (<5 mm) and well-rounded. They are light green and glassy clear. One grain contains oriented linear inclusions. Metal composed of approximately 50:50 kamacite:plessite. Kamacite mostly swathing the olivine. Troilite highly shocked and fine grained. Where troilite and olivine are in contact, the olivine appears brecciated and fragments are distributed throughout the troilite. Interior of the plessite composed of ~75% kamacite and 25% tetrataenite. Within the plessite, the kamacite is dominated by anhedral grains typically 5 to 15 microns across.

Geochemistry: (J. Wasson, UCLA) Metal composition by INAA (mean of two analyses) Ni=76.8 mg/g, Co=5.64 mg/g, Cr=11 μg/g, Cu=164 μg/g, Ga=20.6 μg/g, As=22.8 μg/g, Ru=0.8 μg/g, W=0.2 μg/g, Re=121 ng/g, and Ir=1.42 μg/g. The Ni concentration is the lowest PMG ever measured by UCLA; however, in pallasites Ni is strongly affected by random variations in the kamacite/taenite ratios. Our Ni replicates scattered (90.5 and 63.0 mg/g). The Ir content is the fifth highest in a PMG. No other PMG is closely similar to La’gad 002; the closest is Marjalahti, which also has high Ir (2.1 µg/g) and relatively low Ni (88 mg/g, the eighth lowest). (K. Ziegler, UNM): Analyses of 2 acid-washed olivine subsamples by laser fluorination dual inlet mass spectrometry gave, respectively δ¹⁷O 1.68, 1.777; δ¹⁸O 3.623, 3.861; Δ¹⁷O -0.295, -0.262 per mil (reference TFL slope = 0.528, values are linearized). (L. Garvie, ASU) EPMA analyses of eight olivine grains Fa_13.8±0.1, FeO/MnO=42.0±1.8, Cr₂O₃ to 0.05 wt%.

Classification: Main-group pallasite-anomalous. This stone is likely paired with NWA 10015, NWA 10023, NWA 10252 and NWA 11720 based on the similar Fa and oxygen isotopic values and the high proportion of plessite. The anomalous designation is based on the high proportion of plessitic metal, similar to that in NWA 10023, 10252 and 11720.