Opal is a hydrated amorphous (non-crystalline) type of silica. The process of opalization refers to something turning into an opal — like for example, a big part of this fossil. Opalized ...

Opals! Photonic crystals! Structural color! Opals are examples of natural photonic crystals. They are composed of small silica nanoparticles ranging in size from 50-300nm, and packed tightly together ...

Opal-A: A type of opal characterized by its amorphous structure and the presence of silica nanospheres. Synchrotron X-ray diffraction: A technique that uses X-rays produced by a synchrotron to ...