Australian Opals
FORMATION OF PRECIOUS OPALS - WHAT MAKES AUSTRALIAN OPAL A PRECIOUS GEMSTONE
Opal is the product of seasonal rains that drench dry ground in regions such as Australia’s semidesert “outback.” The showers soaked deep into the ancient underground rock, carrying dissolved silica (a compound of silicon and oxygen) downward.
During dry periods, much of the water evaporated, leaving solid deposits of silica in the cracks and between the layers of underground sedimentary rock. The silica deposits formed opal.
When this silica is deposited slowly under the right circumstances, it forms tiny, microscopic balls. When these balls compact and harden, they form opal. A considerable percentage of this opal is called common opal or potch.
Common opal is truly common. It is found throughout the world. Common opal does not produce the flashes of coloured light we associate with an opal gem.
Something magical happens when those little silica balls settle into a regular lattice-like structure. Light entering the opal is seen back out of the stone in a process called diffraction. The silica balls break up the light into rainbow-like colours.
When this happens, the opal is said to have a play of colour or fire. It is only those stones which have this fire that are considered gems or precious opals.
HOW TO EVALUATE AUSTRALIAN OPALS
The most important factors are:
- What Type (Natural & Synthetic & Reconstructed)
- The Base Colour (White, Crystal, Bolder, Black)
- The Brightness (Colour spectrum, Intensity, Distribution)
- The Weight (Varies for every type of opal)
Precious opal's evaluation should be done under controlled lighting on a dark background.
Rotating the opal against a background helps when you’re determining its type and evaluating its play of colour and cut.
LESS VALUABLE TYPES OF OPAL
OPAL TREATMENTS & SYNTHETICS & ASSEMBLED
Assembled Opal - Altered Opals have no intrinsic & Legacy value
Australian opal can be fragile. In solid opal cabochons, the gem material is usually thick enough to withstand everyday wear and jewellery repair without breaking. Manufacturers often have to add a rigid backing for durability with thinner material.
Assembled opals are fashioned opals with backings. They might include materials like glass that aren’t usually part of gem-quality jewellery, but because they are partly precious opal, they still have value as gems. They sell for only a fraction of the price of boulder opals, but they allow manufacturers to make attractive finished gems from thin opal pieces.
The two common types of assembled opal are the opal doublet and triplet. The doublet is a thin layer of opal cemented to a backing. The backing is often composed of obsidian, dyed black chalcedony, black glass, natural common opal, or plastic. The triplet is a thin layer of opal cemented between a domed top of colorless quartz or clear glass and a backing of obsidian, chalcedony, or black glass.
AUSTRALIAN OPALS - COLLECTORS GALLERY
ONCE IN A LIFETIME - 18.50 CT AUSTRALIAN BLACK OPAL
Ring - Australian Black Opal
THE FAMOUS BLUE-RED Multicoloured 15.46 CT AUSTRALIAN BLACK OPAL
Australian Black Opal - One of a Kind - Exceptional Quality Ring
REMARKABLE 17.20 CT AUSTRALIAN BLACK OPAL
Australian Black Opal - One of a Kind - Red Blue Multi-colour Pendant
EXQUISITE 86.00 CT AUSTRALIAN CRYSTAL OPAL
Australian Crystal Opal - Collectable Extreme Size