About Opal
Not only is it the birth stone of all you October babies, but Opal is a hydrated silica and is classed as a mineraloid rather than a mineral due to its amorphous character.
In all deposits of precious opal, the opal is an infilling of voids (hollow spaces) in host rock, in Australia, these are sedimentary environments. Both precious and common opal are found (often together) filling voids or cavities.
As a result of the natural physical properties of opal, we decided to only ever use Obsidian to back or Doublet as it is also a natural occurring silica.
There are three general types of opal: Precious, common and fire. Here at Jackson Opals, we only work with precious opal. These are identified by the term "Play of Colour" - POC.
Opal may be transparent, translucent, or opaque and the background colour may be white, black, or nearly any colour of the visual spectrum. Black opal is considered to be the rarest, whereas white, grey, and green are the most common.
There are many variant of opal as list below. I have underlined which ones you’ll be able to see here at Jackson Opals.
Types of Opal (May include)
- Australian Boulder Opal (QLD)
- Black Opal
- Nobbie Opal (Lightning Ridge) Nodular.
- Kernel Opal
- Solid/Seam Opal- Natural Homogenous Opal
- Opal in Rhyolite (Volcanic)
- Crystal Opal
- Surface Opal (floaters)
- Opal Replacement (Wood & Fossils)
- Common Opal - no play of colour (POC)
- Contra Luz
By Location:
- Andamooka Opal
- Brazil Opal
- Coober Pedy Opal
- Ethiopian Opal
- Honduras Black Opal
- Hungarian Opal
- Indonesian Opal
- Lightening Ridge Opal
- Lambina Opal (Mines Closed)
- Mexican Opal
- Mintabe
- Peruvian Opal
- White Cliffs
Example of Natural Homogenous opal with skin to skin broad floral pattern- Belemnite Fossil, Coober Pedy, South Australia
Varieties of Cut and Polished Opal may also include:
- Solid
- Doublet
- Triplet
- Inlay Doublet
- Mosaic
- Carved
- Faceted
- Treated (Matrix)
- Imitational
- Synthetic
An example of natural inclusion- POC & common opal (Potch)
Types of inclusions found in opal:
- Potch, or opal without POC, is regarded as an inclusion in the face of a precious opal
- Sand
- Crystals of another mineral - for example, gypsum, or limonite
- Webbing - a spiderweb-like inclusion, sometimes of potch or similar material, throughout the opal
- Ironstone in the face of opal in rock
- Fluid-filled inclusions - water-filled, or sometimes two-phases inclusions with air bubbles in water
An example of natural inclusion- Webbing & common opal (Potch)
Example of natural opal with gypsum veining
Example of inclusion free natural opal- Coober Pedy, South Australia
Example of opal pattern:
