Opal Opal

Solid White Opal

Crystal and white opal are the collective names given to precious opals that are light in body colour.  As its name suggests, crystal opal is the transparent to semi-translucent variety of opal with ‘play of colour’ . The most important source of crystal/white opal is from South Australia,, particularly Coober Pedy and Mintabie,, followed by Lightning Ridge and White Cliffs in New South Wales.

Mohs’ Hardness: 5.5-6.5 / Specific Gravity: 1.25-2.23 / Refractive Index: 1.370-1.470

Black opal

Boulder and black opal are similar in that they both display the darker body coloured varieties of precious opal.  Boulder opal is precious opal that is naturally attached to contrasting dark ironstone matrix creating a dark body colour and is unique to Queensland.  Black opal is precious opal that naturally has contrasting dark body colours of greys, blues or pure black derived from dark potch (non-play of colour opal).  Black opals are the rarest and the most valuable of all opals with Lightning Ridge being the premier source of the world’s best.

Mohs’ Hardness: 5.5-6.5 / Specific Gravity: 1.25-2.23 / Refractive Index: 1.370-1.470

Boulder opal

Boulder and black opal are similar in that they both display the darker body coloured varieties of precious opal.  Boulder opal is precious opal that is naturally attached to contrasting dark ironstone matrix creating a dark body colour and is unique to Queensland.  Black opal is precious opal that naturally has contrasting dark body colours of greys, blues or pure black derived from dark potch (non-play of colour opal).  Black opals are the rarest and the most valuable of all opals with Lightning Ridge being the premier source of the world’s best.

Mohs’ Hardness: 5.5-6.5 / Specific Gravity: 1.25-2.23 / Refractive Index: 1.370-1.470

Opal Doublets

The first opal doublets were made in 1897 at White Cliffs, New South Wales.  Essentially an opal doublet makes use of thin pieces of seam opal otherwise too fragile for use in jewellery by itself.  This is done by adhering it to a contrasting dark base of typically black potch or ironstone creating a look similar to that of black or boulder opal at a fraction of the cost.  As opal doublets are a composite stone, it is important to note that chemicals, heat and even excessive use in water should be avoided.  

Opal Triplets

The evolution of the opal doublet led to the creation of the first opal triplet in the 1950’s.  An opal triplet consists of a solid dark base, usually of black onyx adhered between a razor-thin slice of crystal/white opal and over a protective colourless cabochon cap of either quartz, synthetic sapphire or spinel or Pyrex.  Opal triplets are frequently cheaper than the equivalent opal doublet of similar quality as they use much less opal and labour in their construction.  Like opal doublets it is important to note that chemicals, heat and even excessive exposureto water should be avoided.  O’Neils Affiliated only stocks the highest possible quality, 100% Australian-made opal triplets.

 

 

Opal

General Information

Precious opal is a gemstone that is completely unique, unlike anything else in the world. It displays an extraordinary optical phenomena called “play of colour”; a flashing multi-coloured rainbow against a dark or light background. The best opal in the world comes from Australia, with an orange variety called fire opal occurring in Mexico.

Opal forms when water, supersaturated with silica, comes to rest along bedrock. After being subjected to heat and pressure over millennia, the hydrous silica forms spheres of silica gel, arranged in columns and rows. The more even the size and arrangement of spheres, the higher the quality of the opal. The best opal will display large patches of colour with a high percentage of red on a dark background, though no two pieces of opal will ever be the same.

Quality

Like any gemstone, personal preference is paramount when selecting a gemstone. Whether the opal has lots of red in big patches or a predominantly blue/green pin fire pattern, look for stones without surface reaching inclusions or cracks.

Treatment

Opal can be subjected to various types of treatment. Present industry guidelines state that any method of treatment other than standard cutting and polishing must be disclosed. Types of treatments include colour enhancement, heating, painting, dying, resins and waxes, oiling or any application of chemicals.

Folklore

Ancient lore tells the story of the origin of opal, saying in a fight between gods, the rainbow was shattered and the pieces fell to earth to form opal. In the middle Ages, opal was considered a stone that could provide great luck because it was believed to possess all the virtues of each gemstone whose color was represented in the opal’s colors. In the early 1800’s, a novel by popular author Sir Walter Scott suggested that opal was associated with bad luck and death, and opals popularity halved for the next twenty years. Opal has long been associated with the eyes and vision, and it is believed that opal can convey invisibility on the wearer.

Care

As an amorphous gem material, care must be taken in the cleaning and maintenance of opal. Opal may chip or shatter if struck, is extremely sensitive to heat, and may dry out if stored in hot and/or dry conditions. Warm soapy water is an acceptable cleaning solution and an ultrasonic or steam cleaner must never be used. Opal is very porous, and is susceptible to attack by chemicals or solvents. Opal, like pearls, should be worn carefully.

Scientific Information

Chemical Composition      SiO2 (Silica)

Crystal System                Amorphous

Refractive Index              1.44-1.46

Specific Gravity               1.98-2.20

Hardness                        5.5-6

Cleavage                         N/A

Fracture                          Conchoidal

Lustre                             Vitreous