Coesite is a polymorph of silica that only forms under extremely high pressure -- 10,000 times more on average than normal atmospheric pressure. The presence of this rock at a site indicates either that material has pushed up through Earth's crust from the mantle (a silicate rocky shell between the crust and the core with an average thickness of 2,886 km and depths ranging from 30 km to almost 3,000 km below the crust) or that a celestial body (a comet, meteor or meteorite) fell there. Coesite can also be created by a nuclear explosion.
The mechanism whereby silica (SiO2) is transformed into coesite, which was poorly understood by the scientific community, has now been elucidated by atomistic computer simulation in a study conducted by researchers affiliated with the University of São Paulo (USP) in Brazil; the Chinese Academy of Sciences in Hefei, China; and the Abdus Salam International Center for Theoretical Physics in Trieste, Italy.
Article - Multiple - Pathways - Phase - Transition
The article "Multiple pathways in pressure-induced phase transition of coesite," written by the international cooperative, was published in Proceedings of the National Academy of Sciences (PNAS).
"Coesite is silicon dioxide. Its chemical composition is the same as that of quartz. The difference is that high pressure destructures the crystal lattice characteristic of quartz and compresses the silicon and oxygen atoms into an amorphous system. The result is high-density glass. Once the pressure has surpassed a certain threshold, the amorphization process becomes irreversible and the material can no longer return to a crystalline configuration," said Caetano Rodrigues Miranda, a professor at the University of São Paulo's Physics Institute (IF-USP) and lead author of the article.
Aims - Study - Glass - Application - Horizon
The aims of the study include obtaining what can be called "the best possible glass." There is a technological application horizon due to specific properties relating to thermal conductivity, among others, but for now,...
(Excerpt) Read more at: ScienceDaily