Mysterious crystal with 'forbidden symmetry' found in 4.5 billion-year-old meteorite formed at start of the solar system
- Scientists at Princeton University, New Jersey studied ancient meteorite
- They found a second quasicrystal with a 'forbidden symmetry'
- It was thought such material could not naturally occur in nature
- Crystal has a symmetry in which it shouldn't be possible for atoms to form
- Discovery could shed light on how these materials exist in the universe
A crystal with a ‘forbidden symmetry’ that was once thought to be impossible to form naturally has been found.
The so-called quasicrystal was discovered in a 4.5 billion-year-old meteorite in a remote region of northeastern Russia.
And studying it could help scientists find out how mysterious materials like this formed in the universe.
Scientists at Princeton University, New Jersey studied an ancient meteorite (shown) and found a quasicrystal with a structure that it was once dubbed 'impossible'. It was thought such material could not naturally occur in nature because the crystal has a symmetry in which atoms shouldn't form
The discovery was made by a team from Princeton University, and is the second natural quasicrystal ever found - both in this meteorite.
Prior to the team finding the first natural quasicrystal in 2009, researchers thought that the structures were too fragile and energetically unstable to be formed by natural processes.
‘The finding of a second naturally occurring quasicrystal confirms that these materials can form in nature and are stable over cosmic time scales,’ said Dr Paul Steinhardt from Princeton University.
WHAT IS A QUASICRYSTAL?
On the outside, quasicrystals are solid minerals that look like quite normal, but it is their inner structure that fascinates scientists.
Instead of the regularly repeating clusters of atoms seen in most crystals, quasicrystals contain a more subtle and intricate atomic arrangement involving two or more repeating clusters.
As a result, a quasicrystal’s atoms can be arranged in ways that are not commonly found in crystals, such as the shape of a 20-sided icosahedron with the symmetry of a soccer ball.
The difference between crystals and quasicrystals can be visualized by imagining a tiled floor: Tiles that are six-sided hexagons can fit neatly against each other to cover the entire floor.
But five-sided pentagons or 10-sided decagons laid next to each will result in gaps between tiles.
The team published the findings in the journal Scientific Reports.
Dr Steinhardt said the discovery raises the possibility that other types of quasicrystals can be formed in nature.
Quasicrystals are very hard, have low friction, and don't conduct heat very well - making them good candidates for applications such as protective coatings on items ranging from airplanes to non-stick cookware.
The newly discovered quasicrystal, which is yet to be named, has a structure that resembles flat 10-sided disks stacked in a column.
This type of structure is impossible in ordinary crystals, in which atoms are packed closely together in a repeated and orderly fashion, earning it the ‘forbidden symmetry’ moniker.
‘The structure is saying '”I am not a crystal, but on the other hand, I am not random either,”’ Dr Steinhardt said.
Crystals with these ‘forbidden symmetries’ had been created in the laboratory, but it wasn't until 2009 that Dr Steinhardt and his team reported the first natural quasicrystal, now known as icosahedrite, in a rock that had been collected years before in Chukotka, Russia.
On the left, the top panel shows the symmetry of the first natural quasicrystal called icosahedrite. The lower panel shows the symmetry of the recently discovered quasicrystal, which has not yet been named. Right is the ordered yet non-standard pattern of the quasicrystal revealed by an electron beam
Crystals with these ‘forbidden symmetries’ had been created in the laboratory, but it wasn't until 2009 that Dr Steinhardt and his team reported the first natural quasicrystal, now known as icosahedrite, in a rock that had been collected years before in Chukotka, Russia (shown)
The researchers confirmed that the quasicrystal originated in an extraterrestrial body that formed about 4.57 billion years ago - around the time our solar system formed.
They published those results in the Proceedings of the National Academy of Sciences in 2012.
‘Bringing back the material and showing that it was of natural origins was an important scientific barrier to overcome,’ Dr Steinhardt said.
This new quasicrystal was found in a different grain of the same meteorite and has 10-fold, or decagonal, symmetry.
It is made up of aluminum, nickel and iron, which normally are not found together in the same mineral because aluminum binds quickly to oxygen, blocking attachment to nickel and iron.
The researchers confirmed that the quasicrystal originated in an extraterrestrial body that formed about 4.57 billion years ago, which is around the time our solar system formed (artist's illustration shown)
The researchers are now exploring how the mineral formed.
‘We know there was a meteor impact, and that the temperature was around 1,000 to 1,200 degrees Kelvin, and that the pressure was a hundred thousand times greater than atmospheric pressure, but that is not enough to tell us all the details,’ said Dr Steinhardt.
‘We'd like to know whether the formation of quasicrystals is rare or is fairly frequent, how it occurs, and whether it could happen in other solar systems.
‘What we find out could answer basic questions about the materials found in our universe.’
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