What Are Quasicrystals, How Are They Different From Normal Crystals?
In 2011 Nobel Prize in chemistry was awarded to an Israeli scientist named Dan Shechtman who discovered a type of crystal so strange and unusual that it upset the prevailing views on the atomic structure of matter, leading to a paradigm shift in chemistry.
But Why? What’s So Special About Quasicrystals?
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.
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| A Ho-Mg-Zn icosahedral quasicrystal formed as a pentagonal dodecahedron, the dual of the icosahedron. Unlike the similar pyritohedron shape of some cubic-system crystals such as pyrite, the quasicrystal has faces that are true regular pentagons |
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.
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!
Could this quasicrystal form on Earth?
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.