Meteorites are not flat

If the rock is flat, then it is not a meteorite

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Few meteorites have flat parts. I have been sent photos of meteorwrongs with four kinds of flatness:

  1. Layered sedimentary rocks that are flat on two sides. Meteorites are not layered. Terrestrial sedimentary rocks are layered because Earth has wind, standing water, and gravity. Meteorites come from places with little or no wind, no oceans, and little gravity.
  2. Some igneous rocks fracture along planes leaving a flat surface or two parallel flat sides.
  3. Man-made things that were sawn or forged with a flat side.
  4. Man-made things that started out molten and then solidified in a confined space so that the top is flat or was poured onto a concrete or other hard floor so the bottom is flat.

All of the photos below were sent to me by persons inquiring whether the objects were meteorites. Note that none of these things has a fusion crust.

A flat meteoroid shaped like these rocks would be aerodynamically unstable and not survive passage through the atmosphere with a flat shape. It would break apart. Most of these rocks are sedimentary.
Most of these rocks are sedimentary.
Most of these rocks are sedimentary.
Some kinds of igneous rocks will fracture into pieces with flat sides. Most of these rocks are igneous.
These rocks all appear to have been sawn.
This stuff is probably all man-made. It was once molten and confined in a container. The top was flat, like soup in a kettle. Some of these pieces have flow marks indicating that the liquid was viscous before it solidified.

Two exceptions

Some stony meteoroids break apart during atmospheric entry along planes that can be flat. Here is one of the most spectacular examples that I have seen: Northwest Africa 8371 (L~6 chondrite). Note, however, that it has a fusion crust, the interior is lighter colored than the fusion crust, and all of the edges are rounded.

Lewis Cliff 88023, an ungrouped iron meteorite, is the flattest meteorite that I have seen. It measures 2 x 1.4 x 0.3 cm. I found it during the 1988-1989 ANSMET season in Antarctica. When I showed it to one of my more experienced colleagues I was told, perhaps because of the unmeteorite-like shape, that it was not a meteorite. When I got it back to my lab I sawed off an “end” and discovered that it was metal and had to be a meteorite. It strongly attracts a cheap magnet and contains 6.5% Ni. I doubt that a larger iron meteorite would ever have this beach-pebble-like shape.
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