'Impossibly Perfect' Crystals Found in Nature

June 4, 2009 -- Neither glass nor crystal, quasicrystals have symmetries once considered to be impossible for solids.

Now, 25 years after successfully creating artificial quasicrystals in the lab, scientists from Princeton University and elsewhere have found perfect quasicrystals in nature, locked inside a rock from a Russian mountain range.

"The latest issue surrounding quasicrystals has been could nature ever make them?" said Paul Steinhardt, a professor at Princeton University and a co-author on the paper describing the find, in this week's issue of Science.

"When we make them in the lab we try very hard to make perfect quasicrystals, but nature has no such goal."

Like crystals, quasicrystals have specific shapes that repeat again and again. For crystals there is only one shape (diamond, cube, etc.) that gives a crystal up to six different symmetries. Quasicrystals, on the other hand, have two or more different shapes that repeat but with different spaces in between, giving them beautiful and intricate patterns that are perfectly symmetrical in five, seven, even 12 different dimensions. This high level of symmetry is traditionally forbidden for crystals.

Unlike traditional crystals, however, quasicrystals actually have two geometric structures which enable them to have incredibly complex and often beautiful structures that are symmetrical in five, seven, or even 12 dimensions.

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Laid out on a flat surface, these non-periodic repeating designs are often called Penrose tiles. When wrapped around a 3D object, they become a quasicrystal.

Because their structures are so complex, many scientists thought a quasicrystal could never be created, but in 1984 scientists created the first quasicrystal in a lab.

Over the last 25 years scientists have created more than 100 different kinds of quasicrystals. Some are microns in size while others are inches across. Some are shaped almost like soccer balls, while others look like flower blossoms. They are used in non-stick surface coatings for cookware or in ball bearings.

Most quasicrystals are made from metal alloys. One of the most common alloys used to create quasicrystals in the lab is a combination of iron, copper, and aluminum. The same metal alloy in a repeating crystal structure is what the scientists found locked inside a rock from the Koryak Mountains in Russia.

The quasicrystals found inside the rock are small -- about 200 microns across -- but are nearly perfect replicas of synthetic quasicrystals.

"The fact that quasicrystals formed in nature is interesting in itself," said Tom Lubensky, a professor at the University of Pennsylvania not involved in the research. "Originally it was thought [quasicrystals] were impossible, then they were formed in the lab."

The question of how the quasicrystals got inside the rock is still an open one, says both Steinhardt and Lubensky, but it suggests that an unknown geologic process may be at work. Discovering that process will likely help scientists inside the lab creating quasicrystals as well.

"We don't have a theory that allows us to answer that question yet," said Steinhardt. "There are no rules of thumb. It takes a bit of artistry to create a quasicrystal, and most of them are discovered with a touch of serendipity."

Related Links:

Introduction to Quasicrystals

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