Pink Opal in beautiful rough small chunks.

The mineraloid opal is an amorphous variety of quartz, SiO2 nH2O, hydrated silica with a water percentage of sometimes as much as 20%. Opal can be colorless, white, milky blue, gray, red, yellow, green, brown and black. Often many of these colors can be seen right away, caused by interference and diffraction of light passing through minute, regularly arranged openings within the opal's microstructure known as Bragg's lattice. These gaps are filled with secondary silicic acid and form thin lamellae within the opal during hardening. The term opalescence is used to describe this unique and beautiful phenomenon, although iridescence would be a better term. The opal is one of the minerals that form or can replace fossils. The resulting fossils are spared by collectors. "Opal" is derived from the Old Indian word úpala', which means gemstone. A distinction is made between the glittering noble opals, the yellow-red fire opals and the common opals. Their physical properties show important differences. The opal is the official gemstone of South Australia. Opal has been worked as a gemstone since ancient times. Initially it was used for the manufacture of primitive tools, later for ornamental objects. Opal was already used before the Assyrians, Babylonians and Romans. Noble opal is one of the most mysterious stones. Traditionally it was considered a stone that brings bad luck, especially for people who did not clean the stone properly. The precious opal that Pliny described comes from the deposits of Dubník in Slovakia, which were already being mined at that time. They attributed magical powers to this stone. He helped against melancholy, calmed the nerves, healed the heart, protected from worry, restored sight and gave the eyes a new glow. In addition to naturally occurring opal, opal is manufactured in many different ways, experimentally and commercially. The resulting material is distinguishable from natural opal by its regularity; under magnification patches of color are seen arranged in a "lizard skin" or "chicken wire" pattern. Synthetic opals are further distinguished from natural opal by the former's lack of phosphorescence under UV light. Also, synthetic opals are generally lower in density and often highly porous; some may even stick to the tongue. Two notable producers of synthetic opal are the Kyocera and Inamori companies in Japan. Most so-called synthetic opals, however, are more correctly called imitations, as they contain substances not found in natural opal (e.g., plastic stabilizers). The Gilson opals often seen in fine jewelry are actually imitations consisting of laminated glass with sprinkled bits of foil.