Pallasites


Jaybird Springs (32°08' N 82°59' W)

Jay Bird Springs, Georgia
Find: 2003
Pallasite (main group)

History: A 292 g specimen was found by a farmer (anonymous) near the join of a plowed field and a drainage area ~ 1.5 miles ENE of Jaybird Springs, GA in the spring of 2003. The stone was kept as a curiosity piece until a friend suggested that it might be a meteorite.
Petrography: (T. E. Bunch and J. Wittke, NAU) Very fresh crust with limited iron scaling, a few exposed surface olivine grains may show minor solution etching and are very dark in color. Interior olivine is angular to subrounded with grains up to 16 mm in size. Olivine color varies from grains with light green interior domains surrounded by honey yellow mantles to dark brown grains. Olivine shows a nearly homogeneous distribution within metal and is commonly, partially to completely mantled by troilite whose mantle thickness varies from 0.8 mm to 8.7 mm. Schreibersite occurs as anhedral lumps near troilite mantles together with rare grains of whitlockite and as long rod-shaped grains in kamacite. Taenite occurs as cores surrounded by kamacite. With the exception of the outer most ~ one mm, no evidence of weathering was observed. Some olivines are veined by kamacite and to a lesser extent, troilite.
Mineral compositions: Olivine Fa = 11.9 to 12.9, FeO/MnO = 38 to 44.5. Mean Ni composition of kamacite is 5.8 wt % and taenite is 23.8 wt. %.
Classification: Pallasite (main group).
Specimens: Type specimen of 20.7 and one thin section on deposit at NAU. An anonymous collector holds the main mass.

Jaybird Springs. Width = 3 cm. Image © T. E. Bunch, 2008.


Zinder (13°47'N, 8°58'E)

Niger
Found 1999
Pallasite (pyroxene-rich)

History: A 46 g, mostly crusted meteorite, was found in a field outside Zinder, Niger and purchased in 2001 by a mineral collector. Precise site location is unknown.
Description and classification: (J. Wittke and T. Bunch, NAU) Unusually high abundance of orthopyroxene; modal analyses: orthopyroxene, 28 vol. %; olivine, 27 vol. %; metal, 44 vol. %; sulfide, 1.0 vol. %; chromite, <0.1 vol. %. Olivine, mg# = 89, molar Fe/Mn = 32; orthopyroxene, mg# = 87, Wo2.2; molar Fe/Mn = 20. Metal, Ni = 7.15 wt. %; Co = 0.58 wt. %. Chromite, Cr203 = 60.1 wt. %; molar Cr/(Cr + Al) = 0.85. Weathering grade, W1.
Specimens: main mass with owner; type specimen 5.8 g, one polished mount, and one thin section, NAU (original weight was 9.54 g).

Zinder. Cross-polarized light; black areas are metal. Note the large pyroxene in the upper left quadrant. Image © 2005, Deon van Niekerk.

References

Bunch T. E, Rumble, D., III, Wittke J. H. & Irving, A. J., 2005, Pyroxene-rich Pallasites Zinder and NWA 1911: Not Like the Others: 66th Meeting of the Meteoritical Society Abstracts.


Northwest Africa 1911

Morocco
Found 2002
Pallasite (pyroxene-rich)

Histroy. A 53.07 g complete stone was purchased in Rissani, May 2003.
Classification and mineralogy: (J. Wittke and T. Bunch, NAU): high abundance of orthopyroxene; mineral modes of 8 cm2 (vol. %): orthopyroxene, 34.5, olivine 40.2, metal 24.3, troilite and chromite, 1. Orthopyroxene (mg# = 87.5, molar FeO/MnO = 21.6), olivine (mg# = 89.2, FeO/MnO = 34.5), kamacite (7.35 wt. % Ni), taenite (33.9 wt. % Ni), chromite (59.7 wt. % Cr2O3). Weathering grade, W1.
Specimens: Type specimen, 13.1 g, NAU; main mass, Farmer.

NWA 1911. Gray areas are metal; red/brown parts are pyroxene and olivine. Image © T. E. Bunch, 2005

NWA 1911. Cross-polarized light; Note large orthopyroxenes on the right half of section; black areas are metal. Image © T. E. Bunch, 2005.

Reference

Bunch T. E, Rumble, D., III, Wittke J. H. & Irving, A. J., 2005, Pyroxene-rich Pallasites Zinder and NWA 1911: Not Like the Others: 66th Meeting of the Meteoritical Society Abstracts.


Northwest Africa 2957

Morocco
Found 1997
Pallasite (main group)

History: A 362 g complete stone was found in Morocco in 1997 and purchased by S. Hamani in 1999. The stone was cut in 2003 and the pieces were sold to various dealers and collectors.
Physical characteristics: Lightly weathered fusion crust with a dull to shiny luster. Many olivine grains are cleanly exposed at the surface. Vague ablation-melt features are still visible on the metal surface.
Petrography: (T. Bunch and J. Wittke, NAU) Olivine grains up to 1.8 cm are randomly dispersed throughout the metal host. Schreibersite and merrilite typically occur adjacent to olivine. Olivine is only slightly zoned from core to rim. Metal structure shows large taenite centers with kamacite margins and rare plessitic cores. Small pockets of brecciated olivine, schreibersite and troilite are commonly observed between large olivine grains.
Geochemistry: Olivine cores are Fa11.8 and rims are Fa 12.5, FeO/MnO = 41-44. Taenite Ni = 19.8 wt. % and kamacite Ni = 6.4 wt. %. Schreibersite Ni = 30.5 wt %. Weathering grade is extremely low as are shock effects.
Classification: Pallasite (main group).
Type specimens: Type sample of 21 g is on deposit at NAU. Mr. P. Herrmann holds the main mass of 170 g.

NWA 2957. Gray areas are metal; yellow/brown parts are olivine. Image width 7.2 cm. © T. E. Bunch, 2005.


Other Pallasites

ID Location Date Class. Mass (g) State Fa Fs Comments
NWA 2683 Erfoud, Morocco 2004 PAL 300 S2, W5 10.5 13.8 169 pieces of very large unrecovered mass