At dawn on July 16, 1945, the Earth entered the atomic age with the detonation of
Trinity
, the first nuclear bomb.
In a more discreet way, humans also began a new phase in the history of geology, although they have had to wait 76 years to confirm it: that day the first anthropogenic quasicrystal emerged.
In the wild, this extremely rare type of material has only been seen in meteorites.
Science held until the end of the last century that, leaving glass (which is not a crystal) and amorphous substances aside, all known solid matter had a crystalline structure. In crystals, the molecules and atoms are organized following 230 patterns that repeat periodically, not one more and not one less. But in 1982, Israeli scientist Dan Shechtman discovered something that should be impossible. While researching metal alloys for use in space, he unwittingly created a material that is as organized and stable as glass, but its atomic structure, the way it fills space, follows non-periodic patterns, such as mosaic tiles. or the Fibonacci number sequence. It was the first known quasicrystal. It took Shechtman more than two decades to convince his colleagues.In the end, they had to redo the fundamental theory of crystallography and, in 2011, they ended up giving him the Nobel Prize in chemistry for discovering quasicrystals.
But quasicrystals were not invented by Shechtman, they have existed for a long time, perhaps forever. The same year that the Israeli received the Nobel, his Italian colleague Luca Bindi found in a meteorite that fell in Siberia 15,000 years ago a material whose symmetry was organized by icosahedra (20-sided polyhedra). After its official recognition, it is called icosahedrite. It was the first quasicrystal found in nature. A few years later, Bindi himself discovered another quasicrystalline structure in the same meteorite. It is called decagonite, because its atoms occupy space in decagons. And now the transalpine scientist has done it again. This time discovering the first created by humans.
Most of the trinitite is green and glassy, that is, amorphous. Only a small part is red (in the picture) and only this is a quasicrystal. Luca Bindi and Paul J. Steinhardt.
"The conditions under which the two quasicrystals formed, probably in collisions between asteroids in space in the early solar system, are comparable to those produced during atomic explosions," says Bindi. So he decided to study the material that was formed during the Trinity test. On that day in July 1945, the bomb created a crater 1.4 meters deep and 80 meters wide. The temperature reached exceeded 1,500º and the pressure ranged between 5 and 8 gigapascals. Such extremes vaporized the surface layer of sand, melting it. That's where trinitite was born, a material made up mainly of pale green quartz and feldspar. Something similar happened in Hiroshima, where much of the city ended up turning into beach sand.
But in the Alamogordo desert (New Mexico USA), where the first bomb exploded, there is another rarer trinitite that is red in color. The tone is provided by the copper present. Where did you get the metal from? With the sand, the communications cables (made of copper) and the metal tower from which the bomb fell were also melted and mixed. The first trinitite is a glass, that is, amorphous. The second, the red one, is the one that Bindi has just identified as a quasicrystal, an investigation published in
PNAS
. This material, yet to be named, has base 2 and 3 symmetries, like crystals, but also pentagonal, which rules it out as such.
The crystallologist from the Faculty of Sciences of the Complutense University of Madrid (UCM) Victoria López-Acevedo recalls that “it is impossible for there to be a pentagonal distribution that is also periodic”.
Hence the relevance of Bindi's work, quasicrystals are extremely rare and there are more laboratory than natural identified.
“This is due to the extreme stability conditions.
Diamonds need high temperatures and high pressure and with quasicrystals they have to be much higher ”, he details.
Of natural origin, in addition to those of the meteorite, it has been theorized that some of the fulgurites, the solid materials generated after a lightning strike, could have a quasicrystalline structure.
Quasicrystals are 'quasi' because the three-dimensional arrangement of their atoms is not periodic as in the case of crystals.
Carlos Pina, López-Acevedo's colleague in the UCM crystallography and mineralogy department, says that “it cannot be ruled out that the Chicxulub meteorite impact [the one that killed the dinosaurs] generated some quasicrystal.
In fact, he thinks that "impact craters are good places to look for quasicrystals."
But it also highlights that, being icosahedrite and decagonite of extraterrestrial origin, "no terrestrial quasicrystalline mineral has yet been found."
It could be the red trinitite, but it has been created by an atomic bomb of humans.
Regarding the implications of Bindi's finding, beyond the search for new materials that, like quasicrystals, promise to have many applications, Pina emphasizes that this work reinforces what science knows about “a new way of organizing matter”.
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