(astronomy, geology) A small, shallow indentation or pit on the surface of a meteorite, resembling a thumbprint impression in clay, created by ablation while falling in an atmosphere.Wiktionary
Because of the high-temperature condition of an asteroid falling to the earth’s atmosphere, the surface of asteroid ablated out. This process makes a thumbprint pattern on the surface, called “regmaglypt” or “thumbprint”.
a coating on meteorites that forms during their passage through the atmosphere.Glossary of meteoritics, Wikipedia
When asteroid enters the earth’s atmosphere in multiple-mach speed, the air molecules located in the direction of asteroid trajectory pressurized. Due to the temperature of pressurized air is increased (adiabatic heating). However, these heated air is hot enough, the surface of a meteorite is melting and ablated away by air. Also, a continuous reaction between melts and oxygen, a thin layer of black fusion crust is formed.
Fusion crust is one of the most abundant feature on the meteorites. They are usually black due to the iron content in the stony meteorite. However, they can possess a greenish color (NWA 7325), and gun blue color (iron meteorites).
You may noticed the fusion crust is formed from liquefied asteroid. So it can be flown along the surface of meteorite while it is liquid state.
These flow causes a special surface feature often called “flow line”.
Remarkable surface feature, found in meteorite, is formed by liquefied fusion crust flow to opposite side of entry direction. I think it should be self-explanatory name for it 🙂
This rare feature is rarely found at the iron meteorite, especially the “Sikhote-Alin” meteorite. This stunning feature discovered back to 1998, by J. F. McHone and M. Killgore in Arizona State University and Southwest Meteorite Laboratory, respectively. They claimed this might be formed by the high-velocity collisions between meteoritic particles during the latest stages of atmospheric flight.