Opal

Colour and Varieties

Precious Opal — Opal with play-of-colour on a pale (white opal) or dark (black opal) background.
Fire Opal— Transparent to translucent brwonish-yellow, to ornage, to reddish-Orange; may show a play-of-colour.
Common Opal— Translucent to opaque material with a range of body colours but no play-of-colour.

Opal can be divided into two varieties — precious opal and common opal. Both are fashioned as gemstones, but only precious opal shows a vivid play of iridescent colours for which this gem is prized. Fire opal is named for its colour and water opal for its appearance; both may show a play-of-colour.
Some white opal dispalys a translucent milky appearance and it is this, not the play-of-colour, which is properly termed ‘opalescence’.
Opal is one of the birthstones for october.

The Greeks thought opal gave powers of foresight and prophecy, while the Romans saw opal as a symbol of purity and hope. The Australian aborigines have a legend that opals were born when Earth’s Creator descended to Earth on a rainbow and where his foot first tourched the earth the stones around began to sparkle, displaying all the colours of the rainbow.

Occurrence and habit

Opal is deposited in cavities and fissures in rocks from low temperature, silica-bearing water. Opal may also replace existing structures, such as fossils or soluble minerals.

General and workshop care

Opal is soft so should be treated with particular care. Clean by wiping with a damp or dry cloth only.

Doing anything that could cause abrasion, pressure or knocks.
Heat and dry/hot storage conditions; where possible store with moist cotton balls or a dish of distilled water to avoid dehydration which can lead to cracking and crazing.
Direct sunlight or other strong lights.
Chemicals / acids and detergents, including perfumes, hairspray and make-up, do not soak in jewellery cleaner as opal is porous.
Ultrasonic and steam cleaners
The jewellers’ torch.