For readers who want the full picture
Detailed explanation
The exterior is intensely heated and superficially melted during rapid atmospheric flight. The interior generally remains comparatively cool.
Fresh fusion crust is often dark, but weathering can make it dull, brown or incomplete.
- Typical
- thin, often dark
Not proof by itself
Colour and texture vary with material and preservation. Slag and terrestrial rocks may look similar, so identification requires more than one surface feature.
Formation in a few seconds
Fusion crust forms through ablation during luminous flight. The outermost layer melts, reacts with the atmosphere and solidifies after deceleration. It is normally very thin and does not mean that the whole meteorite melted.
Fresh crust on stony meteorites is often matt to glossy black; iron meteorites may develop it differently. Flow lines record the movement of melt across the surface. Late fragmentation can produce more than one generation of crust.
Ageing and lookalikes
On Earth, oxidation, wind-blown sand, water and temperature changes can turn black crust brown, cracked or incomplete. A pale broken interior beside a dark exterior may be typical but is not proof.
Slag, basalt, weathered pebbles and artificially heated stones can show crust-like surfaces. Genuine fusion crust is assessed together with density, internal texture, metal, minerals and find context.
Short & simple
The essentials in 30 seconds
- A thin surface layer formed during atmospheric flight.
- The exterior is intensely heated and superficially melted during rapid atmospheric flight. The interior generally remains comparatively cool.
- Fresh fusion crust is often dark, but weathering can make it dull, brown or incomplete.
Verifiable
Sources & databases
Editorially paraphrased and expanded from the linked specialist and primary sources; reviewed 24 August 2026. New classifications and database entries may require later updates.