The individual silica nanoparticles (glass beads, basically) are clear, but when packed together in certain configurations ...

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 ...

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 ...