English Opal Cited by user Citation bot on 26 Jan 2019 Opal is a hydrated amorphous form of silica (SiO2·nH2O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%.
English Photonic crystal Cited by user Chris Capoccia on 11 Feb 2018 A photonic crystal is a periodic optical nanostructure that affects the motion of photons in much the same way that ionic lattices affect electrons in solids.