Opal is brittle, heat sensitive, and breaks and scratches
easily. Some varieties self- destruct through the loss of water. Even with
these drawbacks, opal still is a premier gemstone. 
Opal's name evolved from the Roman word opalus from the Greek word opallios -
"to see a change of color." The Greek word was a modification of the ancient
Indian Sanskrit name for opal, upala, which meant "precious stone." If one
spoke in mixed tongues, then opal would be opallios upala, "to see a change of
color precious stone."
As indicated by the derivation of its name, opal has centuries of history as a
treasured gemstone. Historically, beliefs associated with the wearing of opal
have varied.
The early Greeks thought that opals gave their owners the powers of foresight
and prophecy.
Romans adored it as a token of hope and purity.
Eastern people regarded it as sacred.
Arabs believed it fell from heaven.
In the nineteenth century, superstitions grew about the bad luck or fate that
could befall one for wearing opal if it were not the wearer's birthstone.
Today, these superstitions have diminished, but some people still believe it is
bad luck to wear opals.
Opal has over one hundred variety and trade names, but the list of accepted or
commonly used names is much shorter. The most important and most widely known
opal is the precious opal. Precious opal may be subdivided further by color
modifiers, white, black, pinks, and blue, which describe the body color of the
opal.
Australia is famous for its white and black precious opal. Fire opal, the
bright red, reddish-yellow, orange body colored opal is the second most
important opal commercially. Until recently, the best fire opal came from
Mexico. |
Opal - Main Characteristics
| Category |
None-crystalline |
| Hardness (Mohs Scale) |
Six (6) |
| Molecular formula |
SiO2/nH2O |
| Composition |
None-Crystalline solids. |
| Crystal Shape |
Included. |
| Color/Spectrum |
Broad gamma. |
| Atomic (Crystal )Structure
|
None-symmetrical. |
| Index of Refraction |
1.5 |
| Density (Relative) |
2.53 - 2.54 |
| Light interaction |
Opaque-waxy. |
| Uses |
Jewelry, ornamental, other. |
|