Lightning Fast Glass
When two boys stumbled on an unusual rock near Winans Lake, Michigan, they thought they had found what appeared to be at first glance a huge dinosaur leg bone. Scientists from the Museum of Palaeontology at the University of Michigan went out to investigate, only to find that the 15-footlong white, green, and grey object was the world’s largest fulgurite, Latin for “thunderbolt.” It is a tube shaped glob of glass that formed when a powerful lightning bolt struck the ground. The glassy tubes of lightning-fused rock are most common on mountaintops, probably because their high altitude attracts more lightning strikes. Although fulgurites might form from any type of rock, the largest have been created from unconsolidated (loose) sand.
For centuries, scientists have known that large lightning bolts, which can attain temperatures several times those on the surface of the Sun, can melt or vaporize rocks they strike. However, until recently, the chemical and physical processes in the formation of fulgurites were largely unknown. In addition, the studies revealed the presence of two metallic minerals that had never before been found to occur in nature. The fulgurite also was found to be one of the most chemically reduced (oxygen-removed) natural substances known on Earth.
Electron microscope analysis of metallic globules embedded in the fulgurite glass showed them to be composed of a variety of iron and silicon metal compounds previously known only to exist in meteorites. Apparently, the lightning bolt somehow chemically altered the original iron oxides in the ground, to an even greater extent than those found in most meteorites. The fulgurite was also enriched in gold, which the lightning apparently scavenged from the surrounding soil and concentrated in the glass.
A glass of a different sort is in the form of tektites; the name is derived from the Greek tektos, meaning “molten”. They are glassy bodies created from the melt of a large meteorite impact. Over half the rock ejected by an impact remains molten in the rising plume and falls back to Earth as tektites. Much of the high-flying material is known to be deposited halfway around the world. Massive meteorite impacts dump millions of tons of tektites over vast areas called strewn fields.
Tektites range in colour from bottle-green to yellow-brown to black; they were once prized as ornaments by the Cro-Magnon, our ancient human ancestors. Tektites are usually small, about pebble-sized, although a few have been known to be as large as cobbles. Tektites are chemically distinct from meteorites and have a composition similar to that of the volcanic glass obsidian but contain much less gas and water. They also lack microcrystals, a characteristic uncommon in any kind of volcanic glass.
Tektites comprise abundant silica similar to the pure quartz sands used to manufacture glass. Indeed, tektites appear to be natural glasses formed by the intense heat generated by a large meteorite impact. The impact flings molten material far and wide; while airborne, the liquid drops of rock solidify into various shapes from irregular to spherical, including ellipsoidal, barrel, pear, dumbbell, and button shapes. They also have distinct surface markings that apparently formed while solidifying during their flight through the air.
Mysterious glass fragments strewn over Egypt’s Western Desert appear to be melts from a huge impact about 30 million years ago. Large, fist-size, clear glass fragments found scattered across the Libyan Desert were analysed for rare trace elements, which indicated that the glasses were produced by an impact into the desert sands. The large fragments of glass showed extraordinary clarity.
The impact force also generates extremely high temperatures that fuse sediment into small glassy spherules resembling volcanic glass. Thick deposits of sand-size spherules scattered throughout the world document the great meteorite bombardments during the Earth’s entire history.
Joseph Kieffer
http://jewelryuk.org
from: http://hand-crafted-jewelry.com
