So one of the funny things about materials science is that Brilluoin zone diagrams for crystal lattices look like they come straight out of a medieval grimoire.
I cast spell of <111> silicon
Check out the x-ray diffraction pattern image of the reciprocal lattice of icosahedrite. Found only at the blast sites of intense meteorite impacts and nuclear bombs.
What the fuck. The only known naturally occurring example is extraterrestrial in origin, it was brought to earth by a meteorite 4.5 billion years ago.
Showed the icosahedrite diffraction pattern to a coworker and she said, verbatim, "what kind of quasicrystal bullshit is this"
Here's the peer-reviewed PNAS article that pentagram picture comes from.
Ok ok I'm taking off my materials science hat and putting on my science communication hat for a sec. I have a Master's in this field but quasicrystals aren't my forte, so apologies to my PhD followers if I'm off-base.
There's a reason we're reacting like this! To a materials scientist it doesn't just look spooky, it looks wrong. Uncanny valley-wrong, like convincing footage of Bigfoot riding the Loch Ness Monster. For the longest time, nobody believed that 5 sides could happen at all. This was assumed to be completely impossible.
Let me tell u about crystals.
A crystal is an ordered arrangement of atoms. Glass is not a crystal, steel is polycrystalline (individual grains are crystals, but they bump up against each other at misaligned boundaries), salt is a crystal, graphite is a crystal.
Crystals have "rotational symmetry," meaning that there is some way to rotate the pattern and lay it back on top of itself to match. Because of Math and Physics, the only possible rotational symmetries you can get in crystals are two-, three-, four-, and six-fold. Think, like, square or triangular or hexagonal grids, but in three dimensions.
The green image five reblogs back is not a picture of individual atoms, but rather something called a diffraction pattern. You can analyze diffraction patterns to learn how the atoms on a crystal's surface are arranged. That pattern tells us that the atoms of crystalline silicon, sliced along a particular angle called the <111> plane, look like this:
Anyway, two- three- four- or six-fold symmetry, that's it. We long believed that a crystal categorically could not have any other type of symmetry. Crystals were also assumed to be "periodic," meaning that they have "translational symmetry" ā if you shift the entire lattice in particular directions, you could lay it over itself perfectly. Like if you took a sheet of graph paper (four-fold symmetry) and shifted the whole thing one square to the left, you end up with the same sheet of graph paper.
The ominous red image shows a diffraction pattern with five-fold rotational symmetry, which should be impossible. Except, if you could somehow construct a crystal without translational symmetry, you could make it happen. We didn't discover them until the 1980's, and we call them "quasicrystals."
This is an image of what happens to aluminum-palladium-manganese when you do some insane stuff to it with high pressures and temperatures. The quasicrystal is "aperiodic," with no long-range periodicity, meaning that there is no guaranteed way to shift it and rotate it such that it always lines up with itself again. You can spot some local translational symmetries and repeated structures, but they don't hold up over the whole lattice.
In the 1980's, aperiodic tilings were mostly just a fun trick of mathematics. Very few people believed they could show up in real atomic crystals. The unexpected discovery of quasicrystals in 1982 was so wild that Dan Shechtman, the guy who first described them in a sample of aluminum-manganese, won the Nobel Prize.
That's him on the left explaining quasicrystals to a bunch of incredulous and delighted physicists at NIST. This is what physicists look like when they learn something new and exciting, btw, it's pretty great. I love his mustache.
Anyway since 1982, quasicrystals were known to exist only in two places: laboratories, and "trinitite" ā the fused desert sand in New Mexico from the Trinity test, the first atomic bomb. It wasn't until 2010 that we found naturally-formed quasicrystals in that meteorite ā icosahedrite, an aluminum-copper-iron mineral.
Here's the other cool bit: Contrary to what you might expect, icosahedrite likely didn't actually form on impact with the ground! Analysis of the isotopes in the sample indicates that the quasicrystal likely formed in deep space and was brought to Earth in this form[1]. Wild!
Fun fact, aperiodic tilings with a limited number of unique tiles are tricky to make, but they show up in sophisticated art from the Islamic golden age. This is a mosaic in the Darb-e Imam shrine in Iran, built in the 15th century:
Neat!
I love that the red image isn't just aesthetically unsettling, it is also scientifically unsettling
I looked deeper into this all and found a very excellent image of the 2011 expedition to Khatyrka that confirmed that the meteorite was natural in origin
Sadly, I wasn't able to find any info on the indoubtably leading role that this little guy played in the discovery
