Lightning creates strange form of crystal rarely seen in nature: ScienceAlert

The violent fingers of electricity that struck a sand dune in Nebraska left behind a crystal pattern rarely found in nature.

Inside a piece of fulgurite – or “fossilized lightning” – created by a powerful electric bolt traveling through sand and causing it to fuse together, scientists have found a quasicrystal, an arrangement of matter once thought impossible.

This finding suggests that there are previously unknown formation pathways for quasicrystals, opening new avenues for their synthesis in the laboratory.

“The current investigation was designed to explore another possible nature-inspired mechanism for generating quasicrystals: electric discharge,” write a team of researchers led by geologist Luca Bindi from the University of Florence in Italy in their article.

“The discovery of a quasicrystal in a fulgurite with a rarely observed 12-fold symmetry and a previously unreported composition indicates that this approach may also hold promise in the laboratory.”

The Sandhills fulgurite. The quasicrystal was found in the right section. (Bindi et al., PNAS, 2022)

Most crystalline solids in nature, from humble table salt to the toughest diamonds, follow the same pattern: their atoms are arranged in a lattice structure that repeats in three-dimensional space.

Solids that don’t have these repeating atomic structures—amorphous solids like glass—are usually an atomic mess, a jumble of atoms mixed together for no rhyme or reason.

Quasicrystals break the rule – their atoms are arranged in a pattern, but this pattern does not repeat.

When the idea of ​​quasicrystals first emerged in the 1980s, the concept was considered impossible. Solids can be crystalline or amorphous, not that weird in-between. But then scientists actually found them, both in the lab and in nature, deep within meteorites.

Since then, scientists have determined that quasicrystals in nature can only form under extreme conditions, with incredibly high shocks, temperatures and pressures.

Hypervelocity meteor impacts are one such parameter; in fact, for a long time this was the only setting in which they had been found in nature, and thus it was thought that it may have been the only place where they could occur.

Then Bindi and his colleague, physicist Paul Steinhardt of Princeton University, along with their team, found a quasicrystal forged during a nuclear bomb test in 1945. Although not exactly conditions ” natural,” the discovery suggested that there might be other settings in which quasicrystals could form.

Lightning is one of the most powerful forces in nature, striking with extreme speed, and can heat the air it passes through to 5 times the temperature of the Sun’s surface.

And, when it hits the ground in the right place with enough power, it can melt the sand, leaving behind a fulgurite – a “fossil” of the path it traveled through the ground.

All the ingredients are there: shock, temperature and pressure. So Bindi, Steinhardt and their colleagues set out to investigate fulgurites for quasicrystals.

They obtained a sample of fulgurite from the Sandhills area of ​​Nebraska, recovered from a site near a downed power line, and subjected it to scanning electron microscopy and transmission electron microscopy, to determine its composition. chemical and its crystalline structure.

High-angle annular dark-field transmission electron microscopy image of a section of the quasicrystal, demonstrating its order and disorder. (Bindi et al., PNAS, 2022)

The sample consisted of molten sand and traces of molten conductive metal from the power line. Inside, the researchers found a dodecahedral (twelve-sided) quasicrystal with the novel composition Mn72.3Whether15.6CR9.7Al1.8Neither0.6.

The atoms of this quasicrystal formed a pattern with 12th-order symmetry, arranged in a quasicrystalline order not possible in normal crystals.

It is unclear whether the lightning or the power line were responsible for the electricity that created the fulgurite; however, based on their analysis, the team determined that the sand must have been heated to at least 1,710 degrees Celsius (3,110 degrees Fahrenheit) to create the fulgurite.

According to the researchers, this gives clues to how scientists could create quasicrystals in the lab. Quasicrystals Found in Meteorite Suggest Shock Synthesis May Be One Way; lightning offers new possibilities.

“The discovery of a dodecagonal quasicrystal formed by a lightning strike or a downed power line suggests that electric discharge experiments could be another approach to add to our arsenal of synthetic methods,” they write in their paper. .

And the discovery points to pathways of quasicrystal formation that may have been previously overlooked, both on Earth and beyond.

“The results presented here, together with the trace element abundances measured in natural quasicrystals, open up the possibility that electric discharge in the early solar nebula played a key role that not only explains the required reducing conditions, but promotes also the formation of quasi-crystals.”

The research has been published in PNAS.

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