notez le JOUR et la SALLE inhabituels
MARDI 2 Novembre
Résumé :
Throughout the history of geology spanning more than two millennia,
all reported minerals with translational order have had rotational symmetries
restricted to the crystallographic possibilities established mathematically
in the 19th century. However, twenty-five years ago, the concept of quasicrystals
was introduced whose structure has rotational symmetries forbidden to
crystals, including icosahedral symmetry in three dimensions ; and, independently,
the first examples were synthesized in the laboratory. Ever since, an
open question has been whether Nature beat us to the punch : Were quasicrystals
formed through natural geologic processes long before they were discovered
in the laboratory ? In this talk, we will describe the decade-long search
for natural quasicrystals that, through a combination of planning and bizarre
happenstance, led to the discovery last year of the first candidate identified in
a rock found in a remote region of the Kamchatka peninsula. The presentation
will include new evidence that tells us where and how the quasicrystal formed.
RECRUTEMENT ACCES DIRECT
Le département de physique
Fête de la Science 2018 