Different Types of Opal

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PRECIOUS WHITE OPAL
White opal has a light base and can
have strong colour play. Many white
opals can appear rather pale and they
need a closed back bezel setting to
maximise their iridescence.

PRECIOUS BLACK OPAL
Black opal has a dark background
which can be dark blue, dark grey,
dark green or grey-black . The
darker the background the greater
the value of the stone. Black opals
                                                                   are generally rarer than white opals
                                                                   so they have a higher price.

FIRE OPAL  
The colour of fire opal can vary from red to yellow. Orange to
red is the most common with red being the most sought after.
Iridescence is ususally quite rare with fire opals as it has litlle colour.
play. Good quality stones are usually transparent with a vitreous lustre,
they should not be opaque or milky. Unlike most opals fire opals

Below L to R: Precious white opal, black opal, and fire opal.
(For further examples of opal jewellery click here)
  

HARLEQUIN OPAL
Harlequin opal is precious opal which is transparent to tanslucent with
small patches of colour. It is one of the most expensive and desirable
types of opal. It can display a mosaic like pattern of colour.

BOULDER OPAL
Boulder Opal is precious opal that has an ironstone or sandstone
base. Often precious opal is too thin to allow it to be cut to the depth
of the gemstone so the matrix rock is cut with it, making the material
cheaper than pure precious opal. The paler stone has a layer of white
precious opal and the darker stone has a layer of black opal. Due to the
matrix , boulder opal is stronger than precious opal, it is easier to work 
with and can be used in rings.

OPAL MATRIX
Certain opals have a band type growth of precious opal and matrix rock. 
base. There can be small inclusions of matrix rock within the opal.
This results in highly colourful and decorative patterns, with the
deeper ones allowing you to see within the opal. The more detailed
pieces of opal matrix are generally very expensive.

Below: L to R- Harlequin, Boulder, and Crystal Opal
   

CRYSTAL OPAL
Crystal opal is totally transparent and should have
good colour play over the glass like surface. Crystal opals
with both these qualities are rare and expensive.

ETHIOPIAN OPAL
Eithiopian opal has a lovely golden honey colour and can
have great iridescence. It is quite expensive.

ANDEAN OPAL
Andean opal has a bright turquoise, opaque
colour and has become very popular. There have been
issues with Andean Opal in that it can change colour after contact
with air, so now the material is often "fixed" with a glue that covers
the exterior to preserve its colour and make it tougher.

Below L to R: Andean Opal, Cat's Eye Opal, and Ethiopian Opal Ring
    

COMMON OPAL (PRASE OPAL)
Prase opal has an attractive green colour due to the presence of
nickel.It usually has a cloudy appearance and could be mistaken
for chrysoprase

COMMON OPAL (SEASCAPE OPAL)
Seascape opal has a pretty blue-green colour that varies in intensity
and can contain inclusions. The stone has a softness to it  which makes
it only suitable for certain types of jewellery such as necklaces or earrings.

OPAL CAT'S-EYES
It is possible for opal to have a cat's-eye effect (chatoyancy) that is caused
by the reflection of light by parallet channels or fibres. It is quite an unusual
phenomemnon in opal, and large stones are valuable.

   
Above left: Opal gemstone jewellery from Modern Vintage Style
Click here for further technical information on opal