fulgurite

Webster's Dictionary (1913)

Origin: L. fulguritus, p. p. of fulgurire to strike with lightning, fr. fulgur lightning: cf. F. fulgurite.

A vitrified sand tube produced by the striking of lightning on sand; a lightning tube; also, the portion of rock surface fused by a lightning discharge.

Webster’s Revised Unabridged Dictionary (1913), from GCIDE 0.54