Opals are found in many parts of the world.
The opals can be either precious opals or common opals.
Only precious opals are considered to be gem quality.
Opals are formed from a sedimentary process.
Opal forms from watery liquids that have dissolved significant amounts of silica.
If the liquids deposit the silica as they evaporate, then an opal is formed (like setting jelly).
There are three main types of opal, white, black and fire opals.
White opals are the most common type of opal.
Ninety five percent of white opals come from Australia.
Many white opals exhibit a gem phenomena known as color play.
Black opals are much more rare than white opals, and they nearly all come from Australia.
The black opal is any opal that has a dark colored background.
The darker the background the better.
Some opals that are not dark enough are termed semi-black.
Both the white and black opals are polished gems, not cut gems.
The fire opal is a cut gem and looks nothing like its cousins.
The fire opal can be any color from yellow to red.
The fire opal mainly comes from the Yucatan Peninsula in Mexico.
Occasionally some do come from a remote part of Russia.
Famous opals include Big Ben, a precious white opal of more than 4,000 carrots.
The light of the world, a 2,250 carat white opal, is considered to be the most colorful white
precious opal ever found.
Both of these opals came from the opal fields at Lightning Ridge Australia.
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