Analytical market data of rough Australian Opal price per carat USD. How do we calculate this data? CLICK HERE
|MINERAL||SIZE||GRADE||CURRENT||CHANGE||YEAR HIGH||YEAR LOW||AVAILABILITY|
|Australian Opal||10-15 ct||70-90||$35.14||+$0.06||$35.14||$34.79||Moderate|
|Current and historical Australian Opal market price index:|
|Current price per carat by date 2016-2017.||Rough average pricing scale.
Price per carat by year end.
|Physical Properties of Australian Opal:|
|Chemical:||SiO2 · nH2O, Composed of either Cristobalite and/or Tridymite or amorphous silica.||
|Fracture:||Irregular/Uneven, Splintery, Conchoidal|
|Color:||Every color, black, white, and clear.|
|Specific Gravity:||1.98 - 2.25|
|Hardness:||5.50 - 6.50|
|Luster:||Subvitreous, Waxy, Resinous|
|Refractive Index:||1.37 to 1.52|
|Transparency:||Transparent to Opaque|
The internal structure of precious opal makes it diffract light; depending on the conditions in which it formed, it can take on many colors. Precious opal ranges from clear through white, gray, red, orange, yellow, green, blue, magenta, rose, pink, slate, olive, brown, and black. Of these hues, the black opals are the most sought after, whereas white and greens are the most common. It varies in optical density from opaque to semitransparent.
While volcanic-hosted and other types of precious opal are found in Australia, virtually all economic production comes from sediment-hosted deposits associated with the Great Australian Basin. In this basin between 100 million and 97 million years ago, a vast sea began to retreat that covered 60 per cent of Australia. This vast expanse covered Coober Pedy in South Australia to the Gulf of Carpentaria in Northern Australia. This drying out of Australia’s centre increased the acidity levels at shallow depth, releasing silica through the weathering of sandstone. Further weathering then lowered the acidity to a level at which precious opal can form in the silica-rich gel.
The many variations in the types of opal depends on a number of factors. In particular, the climate provides alternating wet and dry periods, creating a rising or more importantly a falling water table which concentrates any silica in solution. The silica itself is formed either by volcanic origin or by deep weathering of Cretaceous clay sediments producing both silica and white kaolin. Special conditions must also prevail to slow down a falling water table in order to provide the unique situation for the production of its own variety of opal.
Most of South Australia’s opal is sold in the rough on the opal fields and exported to Hong Kong, Taiwan, China and other overseas countries for cutting and marketing. However, much of the State’s top quality opal is cut in Australia, generally increasing its value four to five fold, and in some cases by up to 10 times.