Meteorite hunting can be a cruel mistress. Last week I was travelling through Austin Nevada during a trip to my new place of employment. I was a little early to check in at the hotel and decided to visit a nearby playa basin to hunt for meteorites. I was also testing the hypothesis that meteorites could be found nearly anywhere rocks are uncommon and easy to find – salt flat…which was bolstered earlier by reviewing the Meteoritical society’s database of known meteorite find locations.
Google map of the Meteoritical Society's database of meteorite finds.
A front had moved through and there was a fresh coat of snow on the ground a few inches deep. Clouds were boiling on the edge of the basin and zero-visibility blizzards came through more than once that afternoon. I turned off the gravel road and took the truck down the muddy alluvial fan towards the salt flat. After a fun 270 degree spin, I parked and started hiking. Looking around the valley, the salt flat was surrounded by mountains composed of metamorphic and basalt rocks.
Google map of Nevada salt flat
The snow was deep enough to cover most of the ground, but any of the small bushes or scrub had a bare spot at the base. As I walked I noticed that there were no rocks to be found. I must have walked two miles without seeing a single hard rock. Any mud balls or sticks that I came across were sticking up through the snow and transmitted enough ground warmth to melt a bare spot. I figured that if there was a meteorite (or random rock) I would have seen it.
Salt flat
And of course I eventually ran across a couple of tires, thousands of mudballs and sticks, and one rock! I got very excited and immediately picked it up for a look. It was about the size of two baseballs, a greenish colored exterior with red and yellow-greenish mottling and dark veins on the exposed interior. There was also a clearly visible rim on the edge. There are a lot of reasons to think this was a meteorite! Here is a website that describes rocks a lot like mine.
The coloring of the interior is similar to other weathered meteorites I have seen. The reddish color is rusted iron and the green comes from olivine or chondrules. The visible rim was similar to the alteration associated with a fusion crust developed as the meteorite hurtles through the atmosphere and melts the outer surface. If these characteristics were true, it would be consistent with an LL type ordinary chondrite, the most common type of meteorite found.
Figure 1 - Weathering Rim
Figure 2 - Exposed interior top-left, exterior bottom-right.
Figure 3 - Mottling and veins
Closer inspection of the rock convinced me that the rock was not a meteorite. The greenish color of the exterior is very unusual for an ordinary chondrite. The rim on the edge looks a lot more like a weathering rind than a fusion crust. Fusion crusts are typically black and thin. Weathering rinds occur because a rock travels a long way and is exposed to the atmosphere and water that break down the minerals on the outside of the rock. You might expect the crazy random rock that survived the trip all the way down the hill to have a little extra weathering. Finally, the mottling could also be explained by the hematite and plagioclase or olivine that are found in basalt, a rock that could be found uphill. Meteorites can have veins, but terrestrial rocks are a whole lot more likely to have them.
There is one final test. In all honesty, as I type these words I have not yet taken a magnet to this rock. If the rock does have metal in it, the magnet will be strongly attracted to it. The red hematite is an oxide of magnetite, which is also metallic, and could also attract a magnet. However, the strength of the attraction should be easy to tell the difference. Ok, here goes. Nope, not magnetic.
Alright, that’s the test. Its not a meteorite. Meteorite identification is not for everyone, but I like the process. If it had been a meteorite as far as I could tell, the next step to confirming it as a meteorite is to send a portion of it to the closest geology department with a meteorite specialist. At Arizona State University, this would be the ASU Center for Meteorite Studies. http://meteorites.asu.edu/ Once there, a specialist would look at it, considering the mineralogy and structure of the rock. If it passes, the specialist will use an instrument called the PIXE, Particle Induced X ray Emission spectrometer, will be used as the final test to determine if the iron to nickel ratios are consistent with a meteorite. At that point, you then have a real meteorite!
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