All it’s cracked up to be — the fresh fusion crust of a Ghadamis meteorite

This HaH 346 (aka Ghadamis) is my first meteorite with a fresh fusion crust showing differential heating from oriented entry.

Upon entry, the air resistance of rapid entry heats the exterior to melting temperature, hotter than the lava from a volcano. The melted portion is so hot and fluid that it immediately ablates (sloughs off) and new material is melted underneath. Then the meteorite slows and quenches in an instant to a glassy crust. The fusion crust is the thickness of apple skin, and the interior unaffected by heat. If one were to grab it just after landing, it would be cold to the touch, the thermal mass being that of space. The molten rock has a different coefficient of expansion as the underlying rock, and so it cracks from contraction as it cools.

Sometimes, a meteorite like this becomes aerodynamically oriented, finding a stable self-reenforcing angle of attack, like the Apollo Command Module and SpaceX Dragon capsule. So the backside of the stone is shielded from the hottest heating on the front, and shows no signs of cracking (presumably because it does not go through the same degree of thermal shock). Photos of that in comments below.

The black comes from iron in the meteorite, and this one does hold a magnet as a rough check. Fusion crusts usually lack vesicles, but the backside of thid one seems to have them,

This 165g stone is a L6 with W0 weathering. From its MetBull entry: “On 26 August 2018, a large fireball was widely seen and heard around the sparsely populated region of the southern area of the Jabal al Gharbi District of Libya. The fusion crust is fresh and matte black and lacks evidence of extensive wind abrasion. Given the complete lack of weathering of the stones, it is possible that they originated from the 2018 meteor seen in this region.”