Grass Flat        39°40.715’N, 120°56.940’W

California, United States

Find: 1979

Classification: Iron meteorite (IAB-MG)

History: The single mass was found by a Plumas County/California highway construction crew in 1979, during road improvement 2 miles southeast of the town of La Porte, where French Camp Road crosses Slate Creek. Grass Flat is a neaby ghost town. The meteorite had been in the possession of Mrs. Sharon Cisneros, Mineralogical Research Company, for at least two decades prior to the meteorite being sold to Dr. Howard L. McLean in February 2020. An estimated 30 g had been previously removed for classification but that material was reportedly lost.

Physical characteristics: The single, irregularly shaped mass has deep regmaglypts and a dark brown exterior.

Petrography: (C. Herd, UAb) Optical investigation of a ~5 cm × 9 cm polished and etched slice shows a well-defined Widmanstaetten pattern with average kamacite bandwidth of 2.3±0.7 mm (n = 25), consistent with a coarse octahedrite. Two rounded troilite inclusions each at least 2 cm across and rimmed by schreibersite are present in the slice examined. Minor alteration extends along fractures into the interior.

Geochemistry: ICP-MS data, using sample of North Chile (Filomena) as standard (C. Herd and S. DuFrane UAb): Ni = 6.8, Co = 0.462 (both in wt%); Ir = 2.4, Ga = 87, Ge = 294, As = 13, Ru = 5.4, Pd = 3.6, Re = 0.22, W = 1.1, Pt = 6.4, Cu = 144, Au = 1.5 (all µg/g).

Classification: (C. Herd, UAb): IAB iron, Main Group.

Specimens: Type specimen of 69.5 g in two pieces at UAb. Main mass with Howard L. McLean.