Crossword Dictionary
OPAL
opal - n
a translucent mineral consisting of hydrated silica of variable color; some varieties are used as gemstones
Opal is one of the world's most popular gemstones and the birthstone for the month of October. A nice precious opal can flash every color of the spectrum with an intensity and quality of color that surpasses the fire of diamond. The best opals command prices per carat that rival expensive diamonds, rubies, sapphires, and emeralds.
There are many types of opal found in deposits around the world. If you are just starting to learn about opal, here are three varieties that might surprise you: Fire Opal is known for its intense red, orange and yellow colors - the colors of a fire! Boulder Opal is opal with attached host rock. It can be surprisingly beautiful! Common Opal has color, pattern and beauty that can be anything but common. Who gave it such a common name?
Mineralogically, opal is a hydrous silicon dioxide with a chemical composition of SiO2.nH2O. It is amorphous, without a crystalline structure, and without a definite chemical composition (it contains a variable amount of water, as shown by the "n" in its chemical composition). Therefore opal is a "mineraloid" rather than a "mineral."