... Opals stand in a class by themselves. More than any other gem, each opal is distinctly an individual. No other stone has as rich and varied folklore. They are so unique; they have their own descriptive vocabulary. Opals are also the most delicate gems commonly worn. They need special care to insure their health and longevity.
... The name evolved from the Greek "Opallus" which means to see a change in colour. Later, the Latin word "opalus" came to mean precious stone.
... There is some doubt that ancient authors were referring to the same stone we call opal today..
... Opal's fire was long thought to be the result of iridescence. However, with the advent of scanning electron microscopes, we now know that it is a result of diffraction.
... Opal is an amorphous form of silica, (SiO2.nH2O) chemically similar to quartz, (SiO2) but containing 3% to 21% water within the mineral structure. Gem grade opals are usually 6% to 10% water content.
... Opal is a sedimentary stone. Under proper conditions, water percolates through the earth, becoming rich in dissolved silicates. When it enters a cavity, the silicates are deposited as tiny spheres. If they  are uniform in size and shape, they will diffract light. If they are random in shape and arrangement, we have common opal.

... Volcanic ash gives black opal its color, but inclusions have nothing to do with the play of color. That is due entirely to the tiny spheres. They must be smaller than 1500 angstroms for blue and violet colours, but no larger than 3500 angstroms to produce oranges and reds. To put that in perspective, 20,000 spheres are about the size of the period at the end of this sentence.
... Opal grows by filling in cavities, regardless of their shape. Hence, we have many pseudomorphs, materials with shapes that are unrelated to the chemical content. The most common are opalised wood and seashells.

CHEMISTRY SiO₂ . nH₂O. Water usually 6 to 10% in precious opal, can be as high as 21%.
REFRACTIVE INDEX 1.44 - 1.47
HARDNESS 5.5 - 6.5
SPECIFIC GRAVITY 1.99 - 2.25
CLEAVAGE None.
HEAT SENSITIVE Very

Opal Care

             Opals are delicate, but well worth the care. Their most significant weakness has to do with the water content. Keeping them in a tight plastic bag, with a damp piece of cotton or fabric will prevent dehydration. Having said this I have found opal that has been lying on the ground for over 20 years in the blazing hot Australian summers and freezing winters and the stones had not a trace of cracking.
... Storing an opal in oil or glycerine is not recommended. It is unlikely to damage the opal, but it is unnecessary and requires tedious cleaning.
... Because of their water content, opals are also highly sensitive to sudden changes in temperature.
... Opals do not mind being hot or cold, it is the rate of change that damages them, going from a warm house to the winter's cold.... Being somewhat soft, they scratch easily. Realize that a large component of dust is quartz at 7 in hardness. At 5.5 to 6 in hardness, simply wiping the dust off an opal will gradually reduce its polish. The solution is to clean your opals using a soft cloth or brush, a mild detergent, and room temperature water. Then rinse the jewels to remove any residue. Clean doublets and triplets with the same method.
... Prevention is the best solution to scratching and chipping. Opals are best suited for earrings, brooches, and pendants. These jewels receive little contact with harder objects, compared to what a finger ring experiences. If you do get an opal ring, choose a setting that protects it from coming in contact with other objects.
... Understand that, if you wear an opal ring on a regular basis, it will require occasional repolishing. Reserving your ring for special occasions will greatly reduce the risk of damage.
... Make sure you remove your ring before physical activities like gardening and sports

Opal Terms

Play of color, the phenomena of flashing or moving colours due to diffraction and not related to the body color.

Precious opal. Opal with play of color.

Common opal or Potch, translucent to opaque opal without play of color.

Fire in opal refers to play of color.

Fire opal is named for its body color and may or may not have play of color.

Crazing, cracks that develop as an opal dehydrates. Certain areas and fields are worse than others.

Variety Names:

Black opal, precious opal with black body color. Also used for black potch covered with thin layer of crystal opal that lets the black under layer show through.

Gray opal, precious opal with dark or grey body color.

Light opal is in between semi-black and white.

White opal, precious opal with white or very light body color.

Crystal opal, transparent to semitransparent, colourless body with play of color.

Doublets and Triplets make use of opal that is too thin to use as a solid gemstone. A doublet is a thin layer of precious opal glued to a black base. A triplet adds a transparent, quartz cap

.

Black crystal opal, transparent to semitransparent opal, with dark body color and play of color.

Fire opal,  Also called Mexican opal or Sun opal.

Boulder opal, a thin seam of precious opal on ironstone. Since this is a natural occurrence, its value is higher than that of a man made doublet. The ironstone is very dark, which makes the fire stand out and gives a close resemblance to black opal.

Matrix opal consists of thin seams or spots of precious opal in matrix. The matrix is usually dark ironstone, but occasionally a light sand stone, Coober Pedy has a different matrix than other fields a Coober Pedy matrix usually devalues the stone as it has a different shrinkage rate and sends cracks through the opal adjoined to it.

Digging opal is our life

E Mail  sales@desertfireopal.com   for any enquiries.

            Phone / Fax 61 8  86 725 210   (outside Australia )
            Phone/ Fax 08 86 725 210        (within Australia)

Snail mail me :           Darren Underwood
                        Po Box 932
                           Coober Pedy
                              South Australia
            5723

Desert fire opal is located in Coober Pedy Outback  South Australia
Coober Pedy rough and cut opal is what we specialise  in.