What are regmaglypts?
Regmaglypts are smooth, shallow, thumbprint-like hollows on the surface of many meteorites. They are carved during atmospheric flight, as hot gas melts and sweeps away the softer or more exposed parts of the surface.
If you have ever seen a meteorite that looks as though someone pressed their thumbs into soft clay all over it, you have seen regmaglypts. The name comes from Greek words meaning something like "fracture carvings". They are a feature that Earth rocks almost never copy convincingly, which makes them a helpful clue.
They form during the fall. As a meteoroid tears through the atmosphere, the air in front of it becomes extremely hot and the surface melts and blows away, a process called ablation. That heating is uneven. Turbulent swirls in the flow, along with differences in the minerals near the surface, scour some patches faster than others, leaving rounded dents. On iron meteorites, regmaglypts are often especially crisp because metal melts and flows cleanly; fragments of the Sikhote-Alin iron, which fell in eastern Russia in 1947, include some superb examples. Stony meteorites show them too, usually softer and shallower.
The shape and arrangement can tell a story. On oriented meteorites, which kept one face pointing forward, regmaglypts may radiate outward from the front like the pattern on a shield. A meteorite that tumbled may have dents all over. Freshly broken surfaces created late in the fall may have few or none.
Regmaglypts should not be confused with holes or bubbles. They are shallow and open, with smooth rims and a continuous fusion crust lining them, rather than deep round cavities. Rocks with bubbly holes are more likely to be slag or volcanic. Because regmaglypts add beauty and character, well-sculpted specimens are popular with collectors, and they are best kept dry and untouched by wire brushes or chemicals.