Angles and Edges

If a rock has angles and edges but no fusion crust, then it is not a meteorite

For small meteoroids, ~90% of the mass is lost to ablation as they come through Earth’s atmosphere. Edges, “corners,” rough surfaces, and any other protuberances are the first parts to ablate away. Put an ice cube in water and wait for 90% to melt. The “cube” that is left will have no edges or points. It is like that with meteorites. So, if you have a rock with angles and edges, then it is probably not a meteorite.

And, none of these rocks has a fusion crust.
And, none of these rocks has a fusion crust.


Exception

One can easily find photos on the internet of fragments of real meteorites with angles and edges. Here is one:

A sample of the Laundry West meteorite (L4 chondrite). Size of plastic case: 1 inch square? Image credit: Don Edwards and Encyclopedia of Meteorites. Here is a photo of another even more angular sample: Laundry West.

I would not recognize this fragment as self-evidently a meteorite even if someone handed it to me unless, perhaps, I could see rusty metal grains. Most such angular meteorites have broken apart after extensive weathering on Earth. When ordinary chondrites weather by exposure to water and air, the iron metal rusts to iron oxide (oversimplified: 4Fe + 3O2 = 2Fe2O3), which is accompanied by a volume expansion. (This is why the paint over rust on an automobile “blisters.”) The volume expansion is a strong enough force to break the rock apart.

The entire Laundry West meteorite weighs 202 g (wrongly stated as 4 kg in the “Basic information” entry in The Meteoritical Bulletin). The original description (G.J.H. McCall and W.H. Cleverly, 1970) says “five angular fragments totaling 201.9 grams, spread over a linear belt for a distance of 276 feet. The meteorite is strongly oxidised, displaying a smooth, brown, fusion crust… The oxidised state of the mass suggests a considerable age on earth.” Terrestrial ages for meteorites from Western Australia range from <5,000 to 35,000 years. The “spread over” phrase suggests redistribution of the fragments by moving water after the fragmentation.

Irrelevant Trivia Regarding Laundry West

Three meteorites were found in the same area in 1967:

  • Laundry Rockhole, H5 chondrite, 1.44 kg in 32 pieces, June 1967 (map)
  • Laundry East, H3.7 chondrite, 43.1 g in 1 piece, March, 1967, 8 km east of Laundry Rockhole (map)
  • Laundry West, L4 chondrite, 201.9 g in 5 pieces, March 1967, 11 km northwest of Laundry Rockhole (map)

In Australia, a rockhole is a natural depression in rock where water collects. I suspect, but do not know for certain, that Laundry Rockhole was (is?) a place where people cleaned their clothes. Meteorites are named after the place where they are found. In the Nullarbor Plain of southwestern Australia, there are not many named places and the rockhole, apparently, is the most distinctive geographic feature near where these meteorites were found.