fulgurite

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A slender, usually tubular body of glassy rock produced by lightning striking and then fusing dry sandy soil.

Century Dictionary and Cyclopedia

1. n. An explosive of the nitroglycerin class, used for blasting: similar to dynamite, but the nature of the dope has not been disclosed by the inventor.
2. n. A tube formed, usually in loose sand, but sometimes in the solid rock, by lightning; a lightning-tube. Fulgurites are the result of the passage of the electric current through the soil, sand, or rock, producing more or less complete fusion in the vicinity of the path traversed. They usually descend vertically, but sometimes obliquely, find they occasionally branch toward the bottom. They are rarely more than one or two inches in diameter. The effect of lightning is sometimes seen, and occasionally on a large scale, where no proper fulgurites have been formed, but rather a sort of honeycombed condition of the rock, resembling that produced in wood by the boring of the teredo, as observed on Little Ararat, and described by Abich. For the rock (andesite) thus vitrified and altered this geologist proposes the name fulgurite andesite.

Wiktionary

1. n. glass formed by a lightning strike melting sand or other material

GNU Webster's 1913

1. n. 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.