Opal is composed of small beads of silica – alpha-cristobalite – low temperature, but tightly closed in a waterproof casing. Between these “beads” have cavities that contain a small amount of water. Reflection of light on the surface of the opal crystallization gives reflections that differ from each stone depending on the “form” created by all the elements described above. There are many types of opal. Opal can be dull and have no value, in which case such opals called “common opal” because only the large stones of bright colors are “semi-precious opals”.
Type of opal found together with Opal, wearing a certain value, called the Australian “treats”. It has no value as a gemstone; It is used as a basis for simulating a gemstone (ie “synthetic opal”) doublets (based) or triplets (based on coated). Opal “treats” can be white, gray, black, honey, amber or water colors. flickr/David Abercrombie
Opal is one of the most beautiful stones in the world, and, of course, one of the most expensive. Famous contemporary designers often use it in their work. Also, this stone is very rare: some of his views may cost 40 000 euros, and even higher.
Source – Wikipedia