Regmaglypts

Regmaglypts are shallow, thumbprint-like depressions on the surface of larger meteorites that are formed by preferential local ablation of material from the surface as a meteor passes through the Earth’s atmosphere. They are probably formed by vortices of hot gas. Any meteorite with regmaglypts will have a fusion crust. Many meteorites with fusion crusts do not have regmaglypts, however.

Here are photographs of a few examples.  (I collect meteorite photos and do not remember where I obtained some of these photos.)

Lunar meteorite Northwest Africa 482. Regmaglypts are present on the left but not the right. Image credit: Jim Strope

MacAlpine Hills 88108, a 15.4-lb H5 chondrite from Antarctica. Image credit: Randy Korotev

This large meteorite, Lewis Cliff 85320 (H5 chondrite, (244 lbs) has lots of regmaglypts. Photo credit: NASA/JSC

Even this small meteorite (on the ice in Antarctica) has regmaglypts. Photo credit: Randy Korotev

One of the Camel Donga stones from Australia. Photo credit: Jim Strope

Unidentified meteorite found in Nevada with regmaglypts and a grasshopper. Photo credit: I’ve forgotten. Let me know if this great photo is yours.

This is a pretty one. Photo credit: ?

Unidentified meteorite with regmaglypts: Photo credit: ?

Regmaglypts on iron meteorites can be spectacular. Here are small fragments of Sikhote-Alin, an iron meteorite. All of the biggest have regmaglypts. Photo credit: Randy Korotev


Regmaglypts NOT

All the photos below were sent to me by people who thought the rocks had regmaglypts. None of these rocks are meteorites – none has a fusion crust. Some terrestrial processes lead to rocks depressions that can look very much like meteorite regmaglypts. Many of these features are the result of sculpting by wind or water on Earth. Some of the depressions are incipient vesicles. Preferential weathering occurs when softer material weathers away before harder material. This process seems to occur most commonly in sedimentary rocks. Another process is “plucking” in which hard, rounded clasts fall out of a softer matrix leaving a rounded depression.

If there is no fusion crust, then the depression is not a regmaglypt.

 

And, the coating looks much like a meteorite fusion crust, but I think that it is just desert varnish.

 

I’ve seen photos several rocks that appear to be mostly quartz or calcite and that appear to have been preferentially etched by saline solutions solutions leaving a regmaglypt-like surface. The light-colored rock at the top center of the mosaic above is a good example. (If someone knows more about this than me, please let me know.)

 

Geologist would described all of these rocks as “plucked” because the rounded clasts have been plucked (picked out and lost) from the stone, leaving a rounded cavity.