in the last couple of seconds of luminous flight, the molten surface of a meteor solidifies to form a thin, usually black 'fusion crust'.

A thin glassy coating, usually black and rarely exceeding one millimeter in thickness, formed on the surface of a meteorite by frictional heating during atmospheric flight.

(fyoo' zhen krust) - The melted glassy exterior of a meteorite that forms during atmospheric passage. Primary crust is the material that forms from the beginning of incandescent flight until dark flight. Secondary crust forms when a piece breaks off the main mass during incandescent flight and begins to form a new crust on the broken surfaces.