A tube of “fossil lightning” from the Sandhills of Nebraska contains a rare type of quasicrystal previously found only on meteorites and atomic bomb test sites.
Quasicrystals are materials that break the conventional rules of crystallography. Before it was first reported in 1984, scientists thought the material could be either crystalline – with symmetric, repeating patterns – or amorphous, meaning randomly arranged and disordered. Furthermore, scientists believed that crystals could only be symmetric in a limited number of ways when rotated around an axis two, three, four, or six times.
Quasicrystals break those rules. They are put together in an ordered pattern, but that pattern repeats. They also have rotational symmetry that an ordinary crystal cannot achieve. For example, a quasicrystal with icosahedral symmetry may exhibit fivefold symmetry around six different lines of rotation.
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Quasicrystals were first discovered in the laboratory. However, in 2012, Paul Steinhardt (opens in new tab)Luca Bindi, a theoretical physicist at Princeton University and (opens in new tab)A geologist from the University of Florence in Italy announced the discovery (opens in new tab) of a natural quasi-crystal in a meteorite that fell on the Kamchatka Peninsula in northeastern Russia. The researchers then created more quasicrystals in the lab by mimicking the high temperatures and high pressures that can be found when rocky bodies collide. They then moved to another site where high temperatures and high pressures resulted in very rapid transitions: the Trinity atomic bomb test site in New Mexico. There, more quasicrystals were found in minerals from beneath where the atomic bomb had exploded.
“Because of this, I started thinking about other materials that can form under similar conditions. And I thought of fulgurites, materials that form from lightning strikes,” Bindi told our sister website Live Science in an email.
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Fulgurites form when lightning strikes sand, gluing the grains together, in a branched tube of glass. Bindi collects many fulgurites in search of quasicrystals. A carrier of this rare type of case came from the Sandhills of Nebraska, near the village of Hyannis. This area of Nebraska is made up of sand dunes covered with grass.
Fulgurite was found near a power line that fell in a storm in 2008. Overall, it was about 6.6 feet (2 m) long and 3.1 inches (8 cm) in diameter. No one observed this phenomenon, so the researchers are not sure whether lightning struck the power line and formed the fulgurite, or whether the line went down in the air and formed the fulgurite with its own electrical discharge.
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Either way, the resulting vitreous glass contains a mixture of materials from the sand and metals in the power line, including manganese, silicon, chromium, aluminum and nickel. To melt these materials, the sand’s temperature would have to have briefly reached at least 3,110 degrees Fahrenheit (1,710 degrees Celsius), the researchers report Dec. 27 in the journal Proceedings of the National Academy of Sciences. (opens in new tab),
hunting for quasicrystals
Using a scanning electron microscope, Bindi, Steinhardt and their colleagues found a 12-sided, 12-angled crystal with 12-fold symmetry embedded in the fulgurite. Quasicrystals with this type of symmetry are even rarer than quasicrystals in general, the researchers write in their paper; Quasicrystals with 10-fold symmetry or icosahedral symmetry are more common.
Bindi said the discovery points to new places to look for natural quasicrystals.
“This shows that transient extreme pressure-temperature conditions are suitable for the synthesis of quasicrystals,” he said. Other possible places to find quasicrystals, he said, are those formed when large meteorites or asteroids collided with Earth, or in parts of the Moon’s surface that were hit by asteroids.