Samples and analytical techniques

We examined both hand specimens and thin sections DOM meteor- wrongs and compared them with Antarctic igneous rocks (hand samples and thin sections) provided by the US Polar Rock Repository (PRR). The meteor-wrongs include DOM 08301, DOM 14237, DOM 08284, DOM 10165, and DOM 10801. The Antarctic rocks used for comparison were: PRR 46340, PRR46339, PRR7090, PRR13670, and PRR7088, which are all samples of Kirkpatrick Basalts (KB) or Ferrar Dolerites (FD). FD is one of the prominent rocks found in East Antarctica and like a meteorite, it can be round or spherical. Fresh samples exhibit a gray color and have a coarse-grained interior, but with weathering the rock becomes a dark reddish-brown [3]. KB is also a common Antarctic rock and is darker in color (more black than gray or brown) than FD, and more fine-grained [4].

Physical properties of the samples were observed using a variety of techniques. We examined the surface textures of the Antarctic terrestrial rocks using a Zeiss Stemi 305 Stereo Microscope (Figure 2). The density of the DOM hand samples was measured using a jolly balance and the magnetic susceptibility (MS) was determined using a KT-20 Magnetic Susceptibility and Conductivity Meter. We also measured the MS of the PRR hand samples and the minerals magnetite and hematite for comparison.

A Leitz Laborlux 12 petrographic microscope equipped with plane polarized, crossed polarized, and reflected light was used to analyze the mineralogy and petrology of thin sections of both DOM and PRR samples. A tablet camera, mounted onto the microscope, was used to capture images of specific areas of interest within the thin sections.

DOM thin sections were further examined using a Cameca SX 100 electron microprobe. Wavelength Dispersive Spectroscopy was performed using a voltage of 15 kV, a beam current of 20 nA, and a beam size of 10 μm. We used known silicate minerals and metals as standards. Thus far, we have started analyzing samples DOM 14237 and DOM 08301 on the electron probe.

Light microscopy was used to study the optical properties of our unknowns and compare them to our the PRR samples and also a thin section of the Great Salt Lake Meteorite (H5). Both DOM 08284 and DOM 08301 were composed of fine-grained silicates (quartz and feldspar), contained very few oxides, had a grain size of about 10 μm. DOM 10165 had larger silicate grains that measured approximately 150 μm and was abundant in smaller oxide grains. DOM 14237 consisted mostly of quartz and some white and brown grains that measured about 20 μm. Lastly, DOM 10801 was composed of mostly opaque grains in plane light, and in reflected light look to be a mix of hematite and magnetite. Additionally, all DOM samples contained oxides, even if only in trace amounts. The Antarctic PRR samples exhibited massive pyroxene and feldspar grains in igneous cumulate rock textures that measured around 100μm-700μm, with the exception of PRR 46340 which had a grain size around 20μm. The Ant- arctic samples also had a higher range of interference colors indicating pyroxene, has more euhedral grains, and had fewer opaques than our DOM samples. The Great Salt Lake Meteorite looked very different than our DOM samples in that it exhibited angular to subangular grains of highly birefringent pyroxene and olivine, clusters of iron-nickel metal and sulfides, and several decently defined chondrules.

Once again, only DOM 14237 and DOM 08301 have started being analyzed using the electron microprobe. Both samples were composed of anhedral grains of quartz and feldspar with euhedral iron oxides. DOM 142370 was 70% quartz, 20% feldspar, 5% oxides, and 5% alteration minerals (i.e., clays?). DOM 08301 was ~75% quartz, 10% feldspar, 10% oxides, and 5% alteration minerals.