Gem FAQS > Opal > What Is an opal?

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Opals are magic in that they are composed of millions of tiny crystal balls. The name opal comes from the Latin word "opalus" which means precious stone and was revered and valued above all others including diamonds by many. The story goes that Marc Anthony wanted an opal owned by a Roman senator who fled Rome rather than giving up his most prized possession.

Technically opals are amorphous silica and water, SiO2-nH2O. The "n" represents the amount of water, anywhere usually between 3 and 10%. Amophorus means there is no crystal structure but there is a structure throughout each opal. Looking through an electron microscope at 30,000 X the structure of the opal looks like a three dimensional grid of tiny little spheres. The spheres range in size from 150 to 300 nm and are  ideally arranged in hexagonal or cubic patterns.

The size of the silica spheres determine the color you see, small spheres will give you violet and blue color while larger spheres make brilliant oranges and reds.. The more orderly and consistent the tightly packed spheres are organized, the more intense the play of color.

For more detailed check out Wikipedia, Opal .

Last updated on March 15, 2009 by Francis M Lynch