Monday, June 27, 2016

Quasicrystals, .a new thing to know about

I learned something new from the Internet today. It may not be the most useful thing I've ever learned, but it's cool and interesting.
What I learned is that there is such a thing as quasicrystals. A crystal is a mineral that has a defined geometric structure at the atomic level, a structure that repeats itself over and over (i.e. it is both ordered and periodic). In order for such a structure not to break down, it can only exhibit one of four rotational symmetries: two-fold, three-fold, four-fold, or six-fold.
Then, in the 1980s, scientists figured out how to make crystals with five-fold rotational symmetry, crystals that were ordered enough to produce recognizable diffraction patterns when shot with high-energy beams of electrons and x-rays, but that were not strictly periodic (i.e. their organization shifted and changed as they grew), earning them the label quasiperiodic crystals or quasicrystals.
However, no naturally occurring quasicrystals were known, at least until the late 2000s. Two scientists (from Princeton and the University of Florence) found a couple of tiny grains of an unusual aluminium/copper/iron mineral which appeared to exhibit five-fold rotational symmetry, while exploring a sample of the Khatyrka meteorite, an extraterrestrial object, origins unknown, found in the Koryat Mountains of Russia. So, clearly such things are naturally possible in the extreme conditions generated by the falling of a meteorite.
So, there you have it. Quasicrystals. Something to casually drop into a conversation at the gym or the dog park.

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