Sawtooth Knob

Humboldt County, NV USA

Found 06/13/2002

Iron (IIAB)

Two individual masses, 13.44 g and 5.10 g, were found within 100 m of each other, in a dry streambed, by Patricia and Gordon Cave who were prospecting for gold with metal detectors. Both samples were recovered from 4-8 inches depth in soft, dry, desert soil. Both are complete individuals with 2-3 mm diameter regmaglypt-like markings on the exterior. Classification and analysis (D. Hill, LPL): The analyzed sample is mainly kamacite with trace amounts (<<5%) of taenite and schreibersite. No shock deformation is evident. Average compositions from microprobe analysis are: Kamacite, Fe = 93.6 ± 1.4 %, Ni = 5.9 ±  0.6 % (n=536); Taenite, Fe = 72.4 ± 5.8 %, Ni = 26.0 ± 5.9 % (n=111); Schreibersite, Fe = 44.7 ± 6.5 %; Ni = 40.7 ± 5.2 %; P = 14.3 ± 1.8 % (n=94). Width of cross section of a single kamacite lamella ~ 4.3 ± 0.5 mm. The larger, intact specimen indicates octahedral structure with similar kamacite widths. No obvious Widmanstatten structure is visible on the etched surface. Average bulk composition of two replicate INAA samples from the smaller specimen: Ni 6.04 ± 0.06%; Ga 54.6 ± 0.5 μg g^-1; Ge 190 ± 40 μg g^-1; Ir 0.018 ± 0.002 μg g^-1; Au 1.06± 0.01 μg g^-1; W 0.62 ± 0.03 μg g^-1; As 7.94 ± 0.11 μg g^-1.  Based on Ni and other elements, a IIAB designation is indicated, with a closer agreement to IIB irons.  Comparisons of Au vs. Ga, Co, Ir exhibit concentrations that are consistent with IIAB also but do not fall exactly along sample trends noted by Wasson et. al (1998). Type specimens: 2.3 g LPL; 2.8 g + 13.44 g (main mass) Fleischmann Planetarium and Science Center, U. of Nevada.