Tamarack        44°56’2’’N, 116°25’54’’W

Idaho, United States

Found: 10 May 2004

Classification: Iron meteorite (IIAB)

History: Two metallic masses of 16 g and 25 g were found ~15-30 m apart by Mr. Joe Adams using a metal detector, on a grassy, partly forested hill top ~4.3 km southwest of the town of Tamarack, Idaho. Both individuals were completely buried in soil at depths ?1 cm. The smaller individual (measuring ~3 x 1 x 1 cm) was donated to Cascadia and was used for petrographic and geochemical analysis.

Physical characteristics: (A. Ruzicka, Cascadia): The individuals are similar-appearing iron meteorites with prominent regmaglypts and are largely coated by reddish rust stains and a dull brown weathering patina. They have blacker edges and corners (apparent fusion crust) that show exposed metal from the interior at abrasion points. Owing to their proximal recovery locations, similar burial depth, and similar appearance in hand specimen, the individuals are probably paired.

Petrography: (S. Kissin, LHU; A. Ruzicka, Cascadia): Microscopic examination of cut, etched faces reveals primarily kamacite. The apparent bandwidth is ~3 mm, although the specimen observed is too small to obtain a precise bandwidth measurement. Kamacite contains Neumann lines and numerous rhabdites. No traces of a heat-affected zone are preserved in the interior. Microhardness measurements yielded VHN = 208 (mean of 3 measurements, range 202-213), indicating moderate work hardening.

Geochemistry: (S. Kissin, LHU; A. Ruzicka, Cascadia): INAA was performed according to the methods of Wasson et al. (1998) at Activation Laboratories (Ancaster, Ontario), irradiating polished cubes of ~0.4 g and ~3.2 mm thick. This yielded the following elemental concentrations (all units µg/g except where noted): As (10.4), Au (1.09), Co (5.03 mg/g), Cr (20), Cu (103), Ga (74), Ge (370), Ir (0.044), Ni (58.6 mg/g), Pt (4.6), Re (<0.01), Sb (<20), W (<10). These data suggest a Group IIAB designation, although concentrations for Ga and Ge are high relative to other IIAB irons of the same Au content by ~30% and ~230%, respectively, most likely due to analytical error.

Classification: Iron, coarsest octahedrite (IIAB)

Specimens: 14.2 g derived from the smaller sample is available as a type specimen at Cascadia. The owner holds the main mass.