Most of the gemstones that are found are treated artificially either by heating them at a certain temperature or by adding some kind of chemicals in them. But Opal is the only gemstone which does not undergo any type of artificial treatment. http://www.bestingems.com

1. How is an Opal formed
Most of the gemstones that are found are treated artificially either by heating them at a certain
temperature or by adding some kind of chemicals in them. But Opal is the only gemstone
which does not undergo any type of artificial treatment.
Opal, the natural gemstone forms in a very interesting way. It is formed from a combination
of silicon dioxide and water. The stone is truly natural and is formed in a very beautiful
manner. When water runs down through the earth, it collects all the silica present in the
sandstone. This solution is formed by natural decomposition. When the water finally
evaporates under extreme conditions of heat, then it forms small oval structures which take
the shape of an opal when they are hardened.
The silica rich solution which is formed in the volcanic rocks creates cracks and voids by the
weathering process. Many fossils releases molds that acts as a secondary mineral in the
formation of this gemstone. Miners call it by the name of potch and the mineralogist terms it
as Common Opal. During the initial formation, the gemstone is in its unnatural state and
therefore many pores are formed in it.
Variation inside an opal depends upon a number of factors. Climate plays an important role in
the formation in the variation. Wet climate helps to maintain the amount of silica inside the
stone where as a dry climate significantly reduces the water content inside the stone thereby
making it harder. Moreover, regions where volcanic eruptions take place also a material
known as the white kaolin is formed and thereby it helps to produce an Australian Opal.
Many scientists as well as mineralogist are still researching in order to find out the exact way
by which an opal is formed. They are constantly trying to figure out the chemical conditions
or the acidic reactions that are responsible for the creation of an opal. Opals mainly have
their origin from the Great Australian Basin. Three other places that are Lightning Ridge in
New South Wales, South Australia and Queensland boulder where black white and matrix
opals are found respectively.
Another important member in the family of Opal is the Boulder Opal. Even this gemstone is
formed naturally. But the appearance of such kind of opals is quite different. These stones are
generally elongated in shape. They are mainly formed by the accumulation of sandstones.
Matrix and Pipe are the two important opals that are yet other members of the opal family.
Matrix Opal is very rare in existence and they are mainly formed by iron stone. Pipe Opal on
the other hand is like a pipe structure that is usually longer in shape. Hence, Opal Beads are
one of the most natural gemstones that are found on earth.
Semi Precious Stones are found here in abundant quantity. You can order the stones online
and get them at a discounted price.
Source: http://www.streetarticles.com/jewelry-diamonds/how-is-an-opal-formed
Site: http://www.bestingems.com