glossary

The world of Australian Opals is full of colorful terminology. We're eager to share what we know (and learn what we don't). If you come across an unfamiliar term on our site while exploring our unique opal jewelry and it's not defined here, please let us know - we'll add it.

We appreciate your participation in creating a useful reference tool!

Glossary of Terms

Andamooka Opal:

Opal that is sourced from Andamooka, South Australia, is simply called Andamooka Opal. Opal of Andamooka provenance is often treated with with sugar to darken the stone and enhance the contrast of the play of color against it.

Belemnite Opal:

An opal fossil from marine animal most closely related to today's squid and cuttlefish. This ancient sea creature belonged to the cephalopod class.

Black Opal:

Is a natural opal with a body tone or background ranging from semi-black to black.

Body Tone:

The body tone of an opal is independent of its play of color and refers exclusively to its background color. Opal body tone is graded on a sliding scale, starting at N1-N4 for Black Opals, N5-N6 for Dark Opals, and N7-N9 for White Opals.

Boulder Opal:

A natural opal mined in the veins of sedimentary rock in Queensland, Australia. Boulder Opals are cut with the host rock intact, and often display an undulating surface.

Common Opal:

Also known as potch, common opal is opal lacking fire and play of color.

Coober Pedy Opal:

Opal hailing from Coober Pedy, South Australia, is known as Coober Pedy Opal. Regarded as the Opal Capital of the world, most of the opal from this region tends to be either milky white or translucent to transparent crystal opal with play of color running throughout.

Crazing:

A series of fine, interconnected cracks that appear throughout an opal as the stone loses moisture.

Crystal Opal:

The term Crystal Opal refers to any type of Opal - black, semi-black, white, etc - which has a transparent or somewhat translucent appearance.

Diamond - Carat:

Carat refers to the weight of the diamond. The price will go up based the weight and combined with the clarity and cut of the stone.

Diamond - Clarity:

Clarity describes how "clear" a diamond is to the naked eye and with a microscope or jewelers loupe. There are different ranges based on the number of inclusions within a diamond and visibility of the inclusion. There are 6 levels of clarity.

Diamond - Color:

Color grades how "white" the diamond is. The closer to white or "colorless" it is, the higher the price it will command.

Diamond - Cut:

The shape of the diamond combined with the precision in which it was cut from a rough gemstone into the brilliant piece of jewelry. This includes proportions, symmetry and polish. All of this combines to minimize or maximize the brilliance of the piece.

Directionality:

A term that refers to an opal's lack of consistency exhibiting its fire evenly from all angles. A directional opal will appear brighter or have a more intense "play of color" viewed from some angles than from others.

Dugout:

A special type of underground shelter, common to the region of Coober Pedy. By building structures such as their homes, churches and shopping underground, the people of Coober Pedy protect themselves from the scorching summer heat and even the cooler winter temperatures.

Fire Opal:

True fire opals display orange or red body tones, and can often be found in Mexico. The term "Fire Opal" is frequently misused to describe a precious opal with an abundance of fire, however this is a misapplication of the term.

Gilson Opal:

A form of lab-grown opal, this synthetic material was invented by Pierre Gilson In the 1970s.

Hydrophane Opal:

Refers to Opal that absorbs water. Most Ethiopian Opal is hydrophane, although some non-hydrophane exists. When they absorb water, their fire disappears and they become translucent or transparent. After drying out, they *usually* return to their original color. Australian Opals are non-hydrophane.

Natural Opal:

An Opal that has not been treated or enhanced in any way other than being cut and polished.

Mexican Fire Opal:

Of Mexican origin, these opals are most frequently red or orange, but can also be found in shades of yellow and brown. It's a desirable material - though technically considered common opal - and on the rare occasion a specimen displays play of color, it is instead considered Precious Fire Opal.

Opalized Fossil:

When a physical fossil, like a bone, shell, piece of wood or vegetation decays and leaves a cavity that fills with the right solution of silica and water, it can turn into an opal fossil. The opal literally forms inside the space left behind by the former fossil, becoming an opal cast from the mold.

Opal Rub:

Opal Rub is the term applied to a preformed opal that has already been roughly shaped and rubbed to expose its color, but has yet to be fully cut and polished. It's an in between stage to help manage expectations of what the final product might be.

Opalized Wood (Wood Replacement Fossil):

When the roots or branches of decaying trees leave behind a void, it is sometimes filled with a silica solution. As the solution solidifies, it results in an opal mould of the wood particle. This can happen either after complete decomposition of the organic material, or during decomposition, in which case part of the wood's internal structure is forever preserved within the opal.

Play of Color:

The name of the phenomenon that occurs in opals whereby kaleidoscopic colors appear and shift as they dance across the stone's facade.

Pinfire:

A pattern found in some opals that looks like tiny pinhead sized flashes of color. Also described as appearing like "fairy dust" for its mystical and shimmering appearance.

NOTE: Pinfire Opals are among our favorites here at NIXIN Jewelry.

Pipe Opal:

Also referred to as Boulder Pipe Crystal Opal, Pipe Opal is a type of opal that forms in the tubular or "pipe" shaped hollows of its host stone — typically sandstone.

Potch:

A form of non-precious opal, or common opal, it lacks fiery colors and often comes in black, white, grey and shades of brown.

Queen of Gems:

A moniker allocated to Opals, and allegedly coined by William Shakespeare in his play Twelfth Night. The gem was often considered to be miraculous, as it encompassed every color and was believed to harness the virtues of all other gems.

Rough Australian Opal:

Opal specimens extracted from the mine and left in their natural form, neither cut nor polished, are considered rough opal. They may be left in this state and sought by collectors, purchased by cutters, or even used as rough in finished jewelry.

Solid Opal:

A single, solid unit of opal that forms in nature. Its contents are 100% pure, natural opal, and they are not assembled of opal pieces like opal doublets or triplets.