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What is the dark fusion crust on the outside of a meteorite?

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Meteor and meteoroid The Cabin Creek meteorite, an iron (nickel-iron alloy) meteorite that was observed to fall in northwestern Arkansas on March 27, 1886. Its characteristic pattern of “thumbprint” dimples, or regmaglypts, is the result of melting and consequent ablation of its surface as it traveled through the atmosphere. The meteorite is likely a fragment of one of the M class asteroids, which show significant nickel-iron in their surface material.

The dark, glassy layer found on the surface of a meteorite is known as a fusion crust. This feature is a direct result of the intense frictional heating that occurs as the object travels through Earth’s atmosphere at high velocities.12

During this fiery passage, the surface material of the meteoroid melts and vaporizes due to the conversion of kinetic energy into heat. As the object slows down and its luminosity fades, the molten surface material resolidifies, creating the characteristic dark, glassy coating. While the surface undergoes this extreme melting, the interior of the meteorite typically remains unheated.2