Opal Types

Opal is a form of silica, chemically similar to quartz, but containing water within the actual structure. Precious Opal usually contains 6-10% water and consists of small deposits of silica spheres arranged in a regular pattern.

There are six different types of opal to consider:
Black | Boulder | Crystal | Milky | Doublet | Triplet

Layered or Composite Opal

Triplet Opal A three layered gem adhered together comprising first of clear capping usually quartz. Second precious Opal and third a common Opal backing. This process allows for a colourful stone at a fraction of the cost.
Doublet Opal A two layered gem adhered together, comprising first of the precious Opal, this may be either Milky or Crystal Opal. The second (base) layer, a common Opal backing such as brown ironstone. This process is similar to a venire.

Solid Forms of Opal

Milky (Light) Opal Milky (Light) Opal is a solid form of Common Opal. Sandstone and potch (impurities) make up the base of this stone, thus giving it a cloudy or milky appearance. Commonly mined in Coober Pedy, South Australia.
Boulder Opal Boulder Opal is a Solid form of Opal. It comprises of natural Iron stone. This Iron stone is the host structure and often has an undulating surface. Commonly mined in Quilpie, Queensland.
Crystal Opal Crystal Opal is a Solid form of Opal. It is a full silicon base as the host structure. It has little impurity hense allowing light to pass through, giving a translucent appearance. Commonly mined in Andamooka and Mintabie, South Australia.
Black Opal Black Opal is a Solid form of Opal. It has a manganese oxide base as the host structure. The level of manganese is indicated by a index level from N1 being the darkest to N9 the lightest. Black Opal is considered to be the most rare and is mined in Lightning Ridge, New South Wales.