Meaning of "petrified lightning"

vitreous material formed of sand or other sediment fused by lightning.

ful·gu·rite

fo͝ol′gyə-rīt′, -gə-, fŭl′-
ful·gu·rite  (fo͝ol′gyə-rīt′, -gə-, fŭl′-)
n.
A slender, usually tubular body of glassy rock produced by lightning striking and then fusing dry sandy soil.

[Latin fulgur, lightning; see fulgurate + -ite.]

fulgurite

ˈfʌlɡjʊˌraɪt
fulgurite (ˈfʌlɡjʊˌraɪt)
n
(Minerals) a tube of glassy mineral matter found in sand and rock, formed by the action of lightning
[C19: from Latin fulgur lightning]