Monday, July 1, 2013

Petrified lightning

A few weeks ago, one of my aides Octavia told me that lightning hit the side of her apartment building, leaving a strange icicle-like somewhat crystalline formation on the ground reaching about knee-high. I reasoned that the lightning had fused the sand together, but by the time I thought to ask her to take a photograph, the maintenance man had hauled it away. And here I admit to another gaping gap in my paleontological and geological knowledge. When I was researching my post about Dodson's dodo, I saw on the link for the Oxford University Museum of Natural History that they are offering an exhibit of fulgurites, which they bill as split seconds of stormy weather captured in stone. The phenomenon has a name (from the Latin word for thunderbolt) and its fully documented! Lightning – which can reach 3,270 °F (1,800 °C) – melts the grains of sand and the resulting natural glass forms a hollow tube as it cools. The tube can be up to several centimeters in diameter and several meters long, extending into the ground as much as 15m (49'). A blogger who grew up in New Mexico, the "lightning capital of the United States," describes, "In an instant, no more than one second, the white-hot thunderbolt melts and fuses the sand around it and creates an object, a rock, a hardened mass of matter in the shape that the lightning took when it entered the earth. It makes a jagged, plaster-looking cast of itself. Granules of sand cling to these lightning rocks — geologists know them as fulgurite — giving them the appearance of a crusty, crystalline mass. On the outside, they’re not much to look at. The exterior is a mess. Gnarled and knobby....But on the inside, the part you can’t see, it’s pristine. Smooth. Sleek and polished. Molten glass solidified."

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