“Impossible” crystal new to science found in meteorite

The quasicrystal likely formed 300 million years ago while still in space.

Quasicrystals, which violate the mathematical constraints on how crystals are structured, were long thought to occur only when synthetically produced in a lab. Paul J. Steinhardt, a physicist at Princeton University, has been searching for naturally occurring quasicrystals for nearly two decades. Previous finds had already been created in lab conditions, but his latest discovery reveals a quasicrystal that’s entirely new. It was found in a meteorite fragment recovered from a remote site in Russia. We speak with Steinhardt about the story behind what he and his colleagues have discovered.

ResearchGate: What is a quasicrystal?

Paul Steinhardt: Their atoms are arranged with a symmetry that is mathematically impossible for crystals. Crystals have an orderly arrangement of atoms and molecules in which the pattern regularly repeats: like tiles in your bathroom or children’s building blocks when you stack them together. Because of this regular repeating pattern, crystals can only have certain symmetries which constrain all their physical properties.

Quasicrystals have a different orderly arrangement of atoms and molecules that does not regularly repeat and have symmetries forbidden to crystals or crystal patterns. For example, you can make crystal patterns from squares, triangles, hexagons, and rectangles, but not pentagons (or heptagons or 143-agons). Quasicrystals can have five-fold, seven-fold or any-fold symmetry forbidden to crystals.

The meteorite grain containing the newly discovered quasicrystal, which has an icosahedral symmetry. Credit: Bindi et al., 2016

RG: Why is this one special?

Steinhardt: Since 1984, when Dov Levine and I first hypothesized the concept of quasicrystals, and another group independently synthesized them in a laboratory, 100 different types of quasicrystal materials have been synthesized. Until 2009, the only known quasicrystals were those synthesized in the laboratory. Some believed that quasicrystals could only be made synthetically and never in nature.

In 2009, Luca Bindi and I—along with Peter Lu and Nan Yao—reported the discovery of the first quasicrystal found in nature. However, it had the same chemistry and structure as one that had been synthesized in the laboratory in 1987; so it was novel in the sense of being natural, but the chemistry was already known.

The new quasicrystal we’re reporting on now was found in the same meteorite, called Khatyrka. It’s the first example of a natural quasicrystal whose chemistry has never been synthesized previously. Nature made it before humans did!

RG: How did you discover it?

Steinhardt: I started a search for natural quasicrystals in 1998. In 2007, I made contact with Luca Bindi, then director of University of Florence museum, and we eventually found a sample there that included the first natural quasicrystal. Two years later, we had shown that the sample was likely a piece of a meteorite and tracked its origin to a remote site in far eastern Russia (Chukotka). I then organized a geological expedition there to see if we could, by any chance, find more samples. Remarkably, we did. They all come from the same meteorite, which is now officially named Khatyrka. We have been studying each of the grains from the meteorite that we recovered in enormous detail for the last five years, and we recently discovered the new quasicrystal.

The 2011 geological expedition in Chukotka during which the sample containing the new quasicrystal was recovered. Credit: Paul Steinhardt.
The 2011 geological expedition in Chukotka during which the sample containing the new quasicrystal was recovered. Credit: Paul Steinhardt.

RG: How do you think it formed?

Steinhardt: The Khatyrka meteorite definitely contains parts that date back more than 4.5 billion years to the beginning of the solar system. We think one of the three quasicrystals we have found formed at the same time. But the new one being reported here is probably made as a result of a high velocity collision that our meteorite encountered 300 million years ago while it was still in space. We estimate it landed on the Earth less than 20,000 years ago.

The quasicrystals and related metallic aluminum minerals found in the meteorite imply the existence of physical process in the early stages of the formation of the solar system that we did not know before; we are still trying to work them out.

RG: Could this quasicrystal form on Earth?

Steinhardt: Perhaps. We think it is possible to make metallic aluminum minerals deep under the Earth’s surface at ultra-high pressures, the level achieved near the boundary between the Earth’s core and mantle.

RG: Are there any broader implications of this finding?

Steinhardt: Yes, it demonstrates that it’s worthwhile looking to nature for materials and chemistries that we have not yet dreamed of in the laboratory; this inspires us to go to the laboratory to emulate and make variations.

Featured image: Another quasicrystal from the Khatyrka meteorite. Credit: Steinhardt et al.