A beautiful opal is one of a kind: a natural artwork with a unique pattern of rainbow flashes of colour unlike any other. It’s as individual as your personality. You may prefer an opal that serenely glows with pinpoint flashes of the blues and greens of the sea and sky. Or you may fall in love with a gem that flashes broad patterns of red and yellow, with all the bright festivity of carnival in Rio. And with its rainbow appeal, opal complements everything in your wardrobe.
Opal is fascinating to watch, as the colour plays and shifts in its depths. The Mayas and Aztecs called opal bird of paradise stone, and the bright play of colour of this gem does recall the iridescent plumage of these sacred tropical birds. This gem was long thought to have magical powers, from protecting blonde hair from losing its colour to enhancing eyesight.
Opal’s play of colour is created by internal diffraction: tiny silica spheres in grids break up the light into spectral colours, much like the tiny grooves on CDs that shimmer with iridescence. The colours displayed in each stone depend on the size of the spheres: small spheres can only create blue. The largest can show red as well as all the other colours, which have shorter wavelengths.
When opal has a dark background that accentuates its fire, it is called black opal and commands a premium. colour is also more visible when the opal is clear, or “crystal,” rather than cloudy. Opal sometimes forms as a thin layer in ironstone known as boulder opal. Cutters fashion it into free-form cut stones with the opal in front and the natural rock behind. Opal with a light background, called white opal, is one of the most affordable gems.
Opal value is also based on the amount and distribution of play of colour. The ideal is broad patterns covering the surface of the stone, with all the colours of the spectrum, including red, represented. But opals are the most individual of gems and personal taste in colour and pattern should also guide your selection.
The most important source of opal is Australia, which produces the most opal and the finest opal. The legendary locality for the best black opal is Lightning Ridge.
Opal forms in sedimentary rocks when silica-rich water slowly seeps into the host rock, filling seams and crack and hollows. In Australia, this happened about 60 million years ago in the Cretaceous Period. If the water then hits a non porous layer of rock that stops its progress and sits, perhaps for thousands of years deep within the earth, the silica will settle and eventually form a solid gel, trapping the remaining water within its structure. It becomes opal.
Because opals are as individual as a fingerprint, they make a romantic gift. Napoleon gave Josephine a beautiful opal with brilliant red flashes called “The Burning of Troy,” making her his Helen.
Opal is softer than many other gems and should be stored carefully to avoid being scratched by other jewellery. It should also be protected from blows, as exposed corners can chip. Opal should not be exposed to heat or acid. To clean, wipe opal with a soft cloth.