You searched for: “fulgurite
fulgurite (s) (noun), fulgurites (pl)
1. In geology, a glassy, tubular rock structure or crust that is formed when lightning strikes dry sand or unconsolidated sandy soil and causes it to fuse.
2. 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.
3. Etymology: the name was coined in the 19th century from Latin fulgur, "lightning".

Always associated with the sky, bolts of lightning have actually been preserved in sand and rock. These fulgurites, or "petrified lightning", are fragile, glassy tubes formed when lightning strikes in sand, melting the particles around its path and fusing them together.

The hollow fulgurites, or self-portraits of the lightning channels that made them, range from one and a half to five centimeters in diameter. Some fossil fulgurites date back as far as 250,000,000 years.

—Dava Sobel; as seen in The American Heritage Dictionary of Science, 1986.

More about fulgurites

Everyone knows what happens to a tree when it gets struck by lightning, but what about when lightning strikes the ground?

Given the right conditions; such as, sandy soil or a beach, the lightning bolt's path is scorched vertically into the earth, preserved as a network of delicate, glassy tubes.

Knobbly and branched like tree roots, they can penetrate like tree roots and they penetrate several meters.

Estimates of the energy required to create a fulgurite vary, but the temperature reached is thought to be about 4,000 degrees centigrade.

Fulgurites are very rare, and the best place to find them is in shifting desert sand, not only because the necessary raw materials are abundant there; but also, because desert breezes blow their sand covers away.

Fulgurites have a value the goes beyond scarcity and aesthetics: they can exist for thousands of years and are able to provide scientists with information about past climates.

Geologists have discovered another type of fulgurite

High on a mountain in Greenland, geologists discovered another type of fulgurite on a mountain in Greenland: a branched trail running for many meters down a rocky hillside.

Lichen was burned away along the trail and the rock surface was transformed into a smooth glass, colored bright blue, red, and yellow.

This particular mountain top consists of banded rock formations which are rich in iron, and so, definitely not a safe place to be during a thunderstorm.

—Excerpts and modifications from "The word",
New Scientist, June 30, 2007; page 50.
This entry is located in the following unit: fulgur- (page 1)
Word Entries at Get Words: “fulgurite
A glass-like piece of rock formed when lightning strikes dry sand.

Some fulgurites measure up to 10 feet (3 meters) in length.

This entry is located in the following unit: Meteorology or Weather Terms + (page 4)