Regmaglypts
Regmaglypts are shallow dents, like thumbprints, scooped into a meteorite's surface during its fiery fall.
Look closely at many meteorites, especially irons, and you will see their surfaces covered in rounded hollows, as if someone had pressed their thumbs into soft clay. These hollows are regmaglypts, which collectors often call thumbprints.
They form during ablation, when hot, fast-moving air melts and blasts away the outer surface. Weaker spots and swirling airflow eat into the rock unevenly, leaving dimples a few millimetres to several centimetres across. Their shape can show how the meteorite was travelling: on an oriented stone they spread outward from the leading point like ripples. The iron meteorites of Sikhote-Alin, which fell in Russia's Far East on 12 February 1947, are famous for their deep, sharp regmaglypts.
Regmaglypts are a strong hint that a rock is a meteorite, but they are not proof. Weathering can create pits on ordinary rocks, and slag from furnaces is often bubbly in a way that looks similar. True regmaglypts are smooth, shallow and covered with the same fusion crust as the rest of the stone.
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Level: Explorer Ages 10 and up