Opal
Description
Technically described as a mineraloid gel, opal is deposited at relatively low temperatures and may occur in the fissures of almost any kind of rock. Precious opals show a rich interplay of internal colors: these are optical, produced by the interference and diffraction of light passing through the microstructure, which consists of tiny silica spheres packed in a hexagonal or cubic lattice. The source of this image is an Ethiopian opal, consisting of veins of opal deposited in the microfractures of a rock matrix. Opal typically appears in veins like these, leading the jewellery trade to develop novel ways of cutting the material to display its beguiling play of colours.