Flow lines
Flow lines are thin streaks in a meteorite's fusion crust, left by melt that was pushed backwards across the surface during flight.
During atmospheric flight the front of a meteorite is constantly melting. Air streaming past at high speed drags this molten film backwards across the surface, where it freezes as fine ribs or rivulets in the fusion crust. These are flow lines, and they usually radiate from the front of the stone towards its sides and rear.
Flow lines record the last moments of a meteorite's flight. They form best on stones that kept a steady orientation instead of tumbling, so they reveal which face led the way. Because the melt has to freeze before it is blown off, they are also more common on the sides than on the very front. Few meteorites preserve them well. A fine example is Lafayette, a Martian meteorite (a nakhlite) named after the town in Indiana, United States, where it was recognised, whose crust shows streaks of melted rock that flowed back from its leading edge.
To recognise genuine flow lines, look for delicate, roughly parallel threads within a thin crust, all pointing consistently away from one area. Slag and some terrestrial basalts can show flow textures too, so other tests are always needed.
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