One of the world’s most coveted gemstones, Opal’s shifting play of kaleidoscopic colours is unlike any other gem.
When Australia’s mines began to produce opals commercially in the 1890s, it quickly became the world’s primary source for this October birthstone and as I was born in October, this is one of the reasons I named the business Opal Gems.
The technical bit!
Opal is a hydrous silicon dioxide (SiO2.nH2O). It is classed as a mineraloid, because it does not have a truly crystallised structure. The physical structure of Opal is unique. Tiny precipitated spheres of silicon dioxide form a pyramid shaped grid interspersed with water. Tiny natural faults in this grid cause the characteristic play of colour.
Although experts divide gem opals into many different categories, there are two broad classes of opal: precious and common. Precious opal displays play-of-colour, common opal does not. When there is no alignment of uniform silica spheres it is still considered Opal (or Opalite) but there is no flash of colour and therefore called common Opal.
Opals are typically categorised depending on the “potch” (the host rock, also called the “matrix”) on which the opal is formed and their resulting transparency.
Five of the main precious types are:
- White or light opal: Translucent to semi translucent, with play-of-colour against a white or light grey background colour, called body colour.
- Black opal: Translucent to opaque, with play-of-colour against a black or other dark background.
- Fire opal: Transparent to translucent, with brown, yellow, orange, or red body colour. This material—which often doesn’t show play-of-colour—is also known as “Mexican opal.”
- Boulder opal: Translucent to opaque, with play-of-colour against a light to dark background. Fragments of the surrounding rock, called matrix, become part of the finished gem.
- Crystal or water opal: Transparent to semi-transparent, with a clear background. This type shows exceptional play-of-colour.
Today approximately 95% of the world’s opal is sourced from a handful of mining areas in Australia, such as Lightning Ridge and Coober Pedy. Other areas are Brazil, Ethiopia, Mexico, Peru and South Africa.
Examples available at Opal Gems
Peruvian Opal is rare and exhibits an exquisite translucent colouring.
While it typically comes in blue or pink colours, greens are occasionally found.
Coober Pedy White Opal.
The photo shows both the rough opal and irregular cut shapes, ready to be set into a piece of jewellery.
One such common opal is the Pink Opal from Peru, known to the locals as Andean Pink Opal.
The photo shows a Pink Opal cushion cut ring. Pink Opal and Amazonite Ring Stacker Set.
Opals are available on a commission basis.