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Common and fire opal
Apart
from precious opal, there is another type of opa known as
common opal. It is usually fairly translucew cloudy, and without
opal's characteristic iridescence, du. to the fact that the
spheres of silica composing it are to, large. It is generally
rather a dull, pale, unattractive color however, the best
known and appreciated variety, fire opai is brightly colored.
Appearance The color is yellow to orange,
or brilliar scarlet. Fire opal may be a bit cloudy, or almost
perfecti. transparent. For this reason, it is both cut into
cabochor and faceted, unlike precious opal. Transparent specimer
may have good luster. Signs of iridescence are sometime visible
in bright light, the passage from common to noC opal being
continuous, without a clear separation.
Distinctive features Fire opal is strongly
characteriza by its color, combined with an "amorphous"
look, unl,• that of transparent crystalline gems.
It has a very low density, lower than that of glass, w which
it could be confused. On the other hand, it is qi, hard, like
other opals. There is no other stone that rese bles it.
Occurrence It comes mainly from Mexico, but also fr_ Guatemala,
Honduras, and the United States. It is a - found in some parts
of Australia, which is, however, hknown for the more precious
varieties.
Value There is no comparison between the
value noble opal and that of fire opal, which is quite inexpens
. even compared with other minor gems. It is worth so,what
more when a few splashes of color are visible ins the stone.
It is valued by collectors as a curiosity but is i w used
in jewelry.
Simulants and synthetics It
is hard to say whether or r - certain types of glass of a
similar color have been made imitate this modestly priced
gem. It is not produced sy thetically.
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