Pallasite (main group)
History: An anonymous finder
recovered a 1003 kg specimen near Fukang, China, in 2000. The
sample was at the Tucson Gem and Mineral Show in February 2005, and
seen by D. S. Lauretta of UAz. Approximately 20 kg had been
removed form the main mass by the finder before the Tuscon show and
the mass investigated at UAz was 983 kg. (D. S. Lauretta, D. Hill,
M. Killgore, D. Della-Giustina, Y. Goreva, UAz; I. Franchi,
Open U). Petrography and Geochemistry: Olivine Throughout
the large mass, olivines vary in shape from rounded to angular; many
are fractured. They range in size from <5 mm to several cm. The
main pallasite contains several regions of “massive” olivine
clusters up to 11 cm in diameter with thin metal veins only a few mm
in width. Fo86.4 with molar Fe/Mg (0.1367), Fe/Mn
(40.37), and Ni = 0.03 (wt%). Zoning was not observed for Al, Cr,
Ca, Mn, or Fe typical of many olivines in Main Group pallasites.
Metal and Sulfides Groundmass is mostly kamacite with
some occurrences of kamacite mantles surrounding taenite cores,
rounded taenite adjacent to kamacite, and regions of “comb plessite”.
Kamacite contains an average Ni = 6.98 wt%. Schreibersite is
enclosed by wide kamacite bands and as mantles adjacent to olivines.
Two populations of schreibersite are present with Ni = 26 and 35
(wt%) near chromite. Vermicular sulfide (troilite) is present in
some olivine. Thin veins of kamacite and troilite occur inside many
olivines as well. Minor Phases: Euhedral chromites up to 0.5
cm, rounded whitlockite adjacent to olivine, and troilite
heterogeneously distributed in thin veins. Several regions, ranging
from <100 μm to several mm, that contain a complex mixture of
olivine, low-Ca pyroxene, troilite, and whitlockite were observed
adjacent to chromite. Bulk Composition Fe = 89.9 ± 0.3 Ni =
9.0 ± 0.2 P = 0.62 ± 0.02 Co = 0.51 ± 0.01 (all wt.%); Ge = 41 ± 4
As = 26 ± 5 Ga = 19.1 ± 0.5 Pd = 5.1 ± 0.2 Au = 2.6 ± 0.2 (all
µg/g); Ir = 43 ± 4 ng/g. Oxygen Isotopes δ18O =
2.569‰, δ17O = 1.179‰. Classification: Pallasite (main
group). Specimens: A total of 31 kg of sample is on deposit at
UAz. M. Killgore hold a total of 31 kg. An anonymous collector
holds the main mass.
This pallasite is one of the
most beautiful out there. It is known for it's golden-colored large
crystals and fine etch patterns. I finally got my hands on some
superbly cut pieces and here they are.