Welcome to our introduction to the incredible world of Opal and thank you for your interest in discovering Opals I cannot wait to divulge some well kept secrets about what is the #1 most precious, most valuable of all commercially available gemstones. I am very excited about opal and as Opal is experiencing a “Renaissance”. All around the world gem lovers are being drawn to the enigmatic opal. The only gem on earth where you can literally ‘hold a rainbow in your hand’. Precious opal supplies are diminishing. They are a resource that we don’t expect it last much longer, in fact Boulder Opal has nearly all been mined out already! This is a gemstone that is a true investment and (like people) each opal is absolutely unique!
The Rainbow is an eternal, mystical symbol that has captivated our hearts and minds from the beginning of recorded history. Symbolizing the eternal link between earth and the heavens with a Rainbow representing ‘an eternal promise’.
Incredibly rare, beautiful and captivating Opals are the #1 most valuable commercially available gemstone on earth, Australia’s National Gemstone and the state emblem of N.S.W.
Opal has been revered throughout the ages and across the continents with Opal deposits in the Middle East. In the first century it is believed that Hungarian Opals (from Cervenica or Cenowitz) were cut in Idar-Oberstein in Germany and traded back through the silk road (so that the Romans would not invade Hungary and plunder their wealth). Opals have also found their way (through mining or trade) to Mexico, Honduras and Aztec Peru.
Set with translucent White Opals the “Crown of Charlemagne” once adorned the head of the Holy Roman Emperor in the 10th Century. Albert Magnus described the incredible “Orphanus” Opal centrestone: “None like it has ever been seen.. Its hue is as though pure white snow flashed and sparkled with the colour of bright ruddy wine...it is a translucent stone, and there is a tradition that it shone at night-time”.
Mark Antony loved Opal and it is said that he so coveted an Opal owned by Roman Senator Nonius that Mark Antony banished the Senator after he refused to sell the almond sized stone, reputed to be worth 2,000,000 sesterces. Mark Antony is said to have coveted the Opal for his lover, Cleopatra.
The great Roman historian Pliny the elder wrote of the Opal as:
"Having the fire of the carbuncle (ruby or garnet), the glorious purple of amethyst, the sea green of emerald, and all those colours glittering together mixed in an incredible way."
The name “Opal” is derived from the sanskrit Upala “Precious Stone” and the Latin Opalus: “to see a colour change”.
Have you ever held a rainbow in your hand? Opals are the only gems on earth that capture rainbows, literally! A rainbow in the sky is formed because water molecules are trapped in air. In Opal the water molecules are trapped in-between silica molecules.
Opals are the only gemstones in the world where you can 'literally hold a rainbow in your hand'. The amazing thing about Opal that separates them from other gems is that rainbows are actually formed inside the gemstone which is the source of their unique and vibrant rainbow colour patterns. The catalytic process by which silica molecules align in perfect microscopic patterns and structures is still a scientific mystery. What we do know is that water molecules bond with silica forming a new molecule SiO.nH20 (Opal). As the molecules align in geometric patterns that are incredible well structured, aligned and formed (this is the part that Science cannot explain) the molecular process literally forms tiny microscopic rainbows inside the gem, and transforms the rainbow into a gemstone!
Australian Opal does the same thing as a rainbow except the water is stationary rather than moving. Every other gem depends on faceting or chemicals to generate rainbow colours but Australian Opal forms when water (H20) bonds with Silica (SiO2N2) to create a new unique, incredible gemstone we know and love as Opal (SiO2N2H2O). Literally Billions of molecules have to form in perfect alignment in order for the spectacular rainbows to form. If the molecules are scattered, then there is no colour (we call this Opal-without-colour "potch").
When you hold an Opal, you are essentially holding a fossilised rainbow!
Rainbow are formed when water molecules (H20) are suspended in air in a regular enough array to diffract the light that passes through them. As white light is 'split' (when it is slowed down because it has to pass through the water molecules) light splits into the colours of the spectrum, leading to the stunning colours that we know and love as rainbows.
These molecules over time fall (in the form of rain) into the earth, seeping through the soil and attracting silica (or sand) molecules from the outback Australian desert sands. This silica dissolves into the H20, forming a silicate-rich solution known as SiO2nH20. When this solution enters an underground cavity (which is sometimes formed by dinosaur fossils, belemnite, or another form of prehistoric marine animal), the H20 deposits the silicates as tiny spheres in a jelly-like water mass. In extremely rare cases the microscopic spheres are even and consistent in size and perfectly aligned.
The complexity of the molecular array is staggering! To give you an example, if you imagine a silica molecule to be a soccer ball, then an Opal diplaying a range of spectral (rainbow) colours would require a football stadium to be filled with millions and millions of soccer balls, but they would have to be lined up in perfect precision, row upon row, stacked together without any 'out-of-place' to form the precise structures that split the light into the colours of the rainbow.
If the soccer balls were just randomly stacked then the Opal would have no colour (we call this "potch" in the industry).
Opal is formed from silica-bearing waters and can be found inside any type of rock. Throughout the world, silica gel precipitates at low temperatures to form layers or nodules of Opal in fissures, veins, and cavities of volcanic and sedimentary rocks. Opal is an amorphous form of silica (SiO2.nH2O), chemically similar to quartz (Si02), but containing 3% to 21% water within its mineral structure. Opals of gemstone quality usually contain 6% to 10% water. Precious Opal is identified by the defining "play of colors," or the way in which colors change within a particular stone as it is rotated and tilted. Common Opal, sometimes called "potch," is usually colorless or white, but the presence of fine-grained impurities may color it gray, brown, yellow, or red. Potch accounts for 80% to 90% of all Opal, and has no commercial value.
The play of color seen in Opals is attributed to diffraction. Under suitable conditions, water percolates through the earth. Silicates encountered in the soil dissolve into this water to form a silicate-rich solution. When it enters a cavity, the water deposits the silicates as tiny spheres. The layers of precipitated silica spheres form a jelly-like water mass, sometimes producing a diffraction grating when the spheres are even in size and well ordered. The diffraction grating arrangement creates a play of rainbow sparkling light from within the stone. The play of color is due entirely to the uniformity of tiny spheres, each in the order of a tenth of a micron in diameter. If the spheres are random in shape and arrangement, common Opal is formed. If they are uniform in size and shape, they will diffract light and the play of color is evident. The colors caused by the regularly packed spheres making up the internal structure in an Opal depend on the size of the spheres and the voids between them. If you move the stone, light hits the spheres from different angles and you perceive a change in color.
The size of the spheres has a bearing on the color produced. Smaller spheres (less than about 150 nm) bring out blues and violets from one end of the spectrum. Larger spheres (no larger than about 350 nm) produce oranges and reds. These spheres are so small that this size difference translates to a difference between roughly 3 million "larger" spheres and 6.5 million "smaller" spheres lined up within the space of a millimeter. The more uniform the size of the spheres, the more intense, brilliant, and defined the color will be.
This is the 'miracle' of Opal. These millions of molecules have to be perfectly aligned to create a 'diffraction'. With water bonding with Silica between the spheres the spheres diffract white light, breaking it up into the colours of the spectrum. This process is called 'Opalescence'. Larger spheres provide all colours, smaller ones only blues and greens. Opals that have a predominantly red colour are very rare as they only occur where larger silica spheres were deposited.
The "Bragg diffraction grating" is the refraction of various wavelengths (approximately the same wavelength as the diameter of the spheres) giving rise to the various flash of different colors.
Australia is the only part of the world where Opalised animal and plant fossils have been found
The Australian Opal fields were once an inland sea. As the ages passed and the seas receded, sea creatures were isolated and marooned, and Opalised. Eventually the area dried out completely and is now dry desert country. In time the ground waters, holding silica solution, also evaporated (with some artesian springs still active deep "underground"). Opal is formed as water runs down through the earth picking up silica from sandstone. This silica-rich solution is then carried into cracks and voids, caused by natural faults or decomposing fossils. As the water evaporates, it leaves behind a silica deposit. The deposit eventually hardens to form common Opal, and in rare circumstances it forms precious Opal.
At Lightning Ridge in NSW, small Opalised dinosaurs and primitive early mammalian remains, together with shallow marine shellfish and crustaceans have been found. Probably the most famous Opalised fossil is Eric the Pliosaur (Cretaceous age marine vertebrate) which was found at Coober Pedy and now forms part of the Australian Museum collection.
Not only is the Opalised skeleton of this animal preserved, but also the stomach contents of its last fish meal are replaced with Opal. Opalised fish bones and shelly mollusks are also fairly common at Coober Pedy, SA and are valued according to the appearance of the individual specimen and the intensity of the play of colours.
Spectacular mineral replacement with Opal can also occur. The so called 'Opal pineapples' found at White Cliffs, NSW are Opal pseudomorphs of the mineral glauberite are examples of this. Queensland Opal deposits occur in non-marine sedimentary rocks and Opalised animal remains are very rare, however fossil wood fragments showing annual growth rings and cellular wood textures occur and sometimes these are beautifully replaced with precious Opal.
Opal is an extremely precious gem. Black Opal is possibly 130 times rarer than diamond! For every 130 million carats of diamond produced only 1 million carats (or 200kg) of Opal is mined. And from this rough the loss factor in cutting can be as high as 95% (In black Opal).
You may have heard that "Tanzanite is 1000 x rarer than diamond". This is suggested because there are 100 miles of tanzanite mines worldwide, and when compared to the 100,000 miles of diamond mines worldwide "Tanzanite is 1000 x rarer than diamond". As there is only 20 square miles of black Opal mining black Opal is actually 5000 x rarer than diamond.