What is Black Opal?

What is Black Opal? 

What is Black Opal is a question I’m often asked by friends living in Australia and my friends who live abroad in the United States, Canada, and the UK. So when my friends hear the word “black” they naturally assume that the black opal is black and often ask me this question “what makes a black rock so rare and incredibly spectacular”? Hmm, a good question, a question we will find out the answers to a little further down the page…

The Beginning

So let’s take a little look into the beginning of Australia’s national gemstone, the Opal. The formation of Opal began millions of years ago when an inland sea covered the central part of Australia. This sea provided our Earth with silica-rich deposits that found their way into cracks, voids, and decomposed fossils as the result of water flowing down through overlying sandstone. And to this day we are finding marine fossils and opalised marine fossils in inland parts of Australia hundreds of miles away from any coastline.


Now if you happen to purchase an Opal through our website, or you currently own a solid Opal, jot down the measurements and remember this: Palaeontologists estimate that it takes approximately 5-6 million years for a 1 cm thick Opal vein to mature.  WOW, just imagine how ancient your Opal could be.

What is Black Opal? 

  • Unlike Diamonds, Opal is a non-crystalline, hydrated amorphous form of Silica, created by the combination of Silicon Dioxide (Silica & Oxygen) with water Si02.nH2O.
  • The moisture content of Opal varies between 3 to 21 percent by weight, but the ideal range is between 3 to 10 percent.
  • Quality Australian Opals contain around 5-6 percent water by weight.
  • Crystalline forms of Silica are minerals. However, Opal is a mineraloid because it has no defined shape or crystalline structure (amorphous).
  • Opals have a relative hardness value of approximately 5.5 on the Mohs scale which is about the same as glass.
  • Opal, in my opinion, is a bit more fragile than glass so avoid contact with any hard surfaces.
what is black opal
Black Opal Stone

What is Black Opal? – Internal Structure

The internal structure of Black Opal is made up of microscopic spheres of Silica approximately 0.00005 – 0.0004 mm in diameter, that have grown around a central nucleus. Viewing these
minuscule areas of Silica requires the use of an electron microscope with 30,000x magnification.

The Silica spheres are what orchestrates the amazing and unique light shows that captivate audiences from all over the World.

Australian black opal fire
Cmglee – Creative Commons

The size of the diameter of the hydrated Silica spheres determines the ‘play of colour’ by causing white light to refract and diffract.

Example 1. Diffraction – light waves bend as they pass the edge of an object and around small particles. Within Opal, the light turns around tiny spheres of hydrated Silica and Oxygen and can create the entire spectrum of colours.

Example 2. Refraction – when light travels from one medium that has a different density to another, light changes direction. Unlike a diamond, Opal doesn’t have a definitive Refractive Index (RI) because the refractive indices of the spheres of hydrated Silica vary. Therefore, the Refractive Index measurement for Opal can range between 1.37 – 1.52.

You can see in example 1, the longer wavelengths of red, diffract more than the shorter wavelengths of violet. In example 2, the shorter wavelengths of violet refract more than, the longer wavelengths of red.

Diffraction bends waves; refraction changes the direction and speed of the waves.

Brilliant and captivating colours display when light waves travel through the transparency of Silica, and it is possible for all the colours of the spectrum to be visible within just one stone. I know, because I have a 2.86 carat solid Black Opal that displays every colour you can imagine. And this gemstone takes me to another world.

  • Most Opals consist of spheres of hydrated Silica less than 0.00025 mm in diameter. But precious Opals consist of larger silica spheres, which arrange in an orderly pattern creating spaces between the spheres.
  • An irregularly stacked, non-uniform in size opal, with no-show of colour, is called potch. This form of Opal is most often made up of silica spheres as tiny as 0.0001 mm in diameter. These hydrated Silica spheres are way too small for light to diffract. Potch is a common Opal and the nucleus for precious opal to form.
  • Smaller-sized spheres produce violet colours.
  • Medium-sized spheres create blues and greens.
  • The rare colour of red is the result of larger spheres 0.0003 mm in diameter.

What is Black Opal? – Characteristics (C’s) 

A Diamond has four characteristics (4 C’s), however, Opal has many features including:

Opal type

  • Black 
  • White
  • Crystal
  • Boulder
  • Matrix
  • Pineapple

Crystal Opal – is the only form of Opal that does not contain potch and is transparent when put up to light.

Body Tone 

  • The shade of the body
  • Darker tones display more vibrant colours


  • Faint:  1/5
  • Dim:  2
  • Somewhat Bright:  2.5/5
  • Bright:  3/5
  • Quite Bright:  3.5/5
  • Very bright:  4/5  
  • Extremely Bright:  4.5/5
  • Brilliant:  5/5


  • Opaque
  • Translucent
  • Transparent


  • Predominant hue 50 – 70 percent
  • Secondary hue – 20 percent


  • The richness of colour


  • The depth and amount of fire


  • Display of colour when rotated


  • Large, vivid and clean adds value


  • Marks and inclusions lower the value

Carat Weight  

  •  One carat (1 ct) = 200 mg  

Shape & Proportion

  • Symmetry and shape can have an influence on gemstone price.


If you love gemstones you will love the Australian Black Opal. And within our website, you will find an amazing array of solid Black Opal Stones waiting for someone special like you to give them a home. Of all the different Opal types, the Black Opal is the most valuable because of its rarity and characteristics. Distinguished from other Opals by its darker body tone, the Black Opal actively enhances the refraction, diffraction, and reflection of light. And the most valued colour in Black Opal is the red fire which can fetch a price of up to Aud $20,000.00 for a carat.

what is black opal

Thank you for stopping by and I hope you’ve enjoyed the information presented in this article.

For any questions, additional information or to make a comment, please do so in the comments box.

And finally, if you can let me know from which country you are from, that will be great.

Thanking you…

Related Links
Lightning Ridge black opal
Australian black opal pendants
Lightning Ridge opal mining

Australian Black Opal Stone

The Lightning Ridge Black Opal

Australian Black Opal Stone – The Birth of Black Opal

The birth of Australian Black Opal Stone began around 600 to 500 million years ago when the suturing of the ancient continent Gondwana evolved.

Gondwana was an incredibly massive continent incorporating many land masses that are now part of our Southern Hemisphere. Lands forming this ancient continent included the Indian subcontinent, the Arabian Peninsula, South America, Africa, Madagascar, Antartica, and Australia.

In the ancient times of Gondwana, an inland sea producing significant amounts of silica-laden sediment covered the central part of today’s Australian continent. The presence of this inland sea provides the seed for the birth of Opal by depositing vast quantities of Silica into small cracks in rocks (voids), decomposed fossils, and in layers of clay. In summary, Black Opal is the result of water flowing down through the earth and picking up silica from sandstone on the way. The water evaporates and the silica-rich deposits are left behind creating a path for the birth of opal.

Silica naturally nourishes our marine environment and the many marine fossils, fish bones, and shells found in central Australia confirm the existence of this Silica bearing inland sea.

Australian Black Opal Stone – The Legend

Sanskrit is an ancient language in Hinduism, and there is the belief that the English word Opal, evolves from the Sanskrit word upala, meaning ‘valuable or precious stone.’

The name Opal may also be associated with the Greek word opallios, meaning ‘to see a change in colour’. The ancient Greeks also believed Opals (opallios) to be the ‘Tears of Zeus.’

The ancient Australian Aborigines believed the opal to be half serpent and half devil. The beauty of the fire colours within the stone would lure and trick someone to enter the demon’s den.

Today, the Aboriginal legend tells the birth of opal happening when the footprint of the creator touched the earth at the base of a rainbow to bring harmony.

Australian Black Opal Stone – Wallangulla (LR)

The Australian black opal

Black Opal stone is native to Australia. It is unique and rare. And you can only find this precious gemstone in Lightning Ridge and the surrounding Opal fields of the Wallangulla region in outback NSW, Australia.

Located approximately 730 km north-west of Sydney and 730 km south-west of Brisbane, Lightning Ridge (LR) has no traffic lights and is home to the Black Opal.

Lightning Ridge is the only place in the World where black opal is commercially produced and for more information on opal mining in Lightning Ridge please visit Lightning Ridge opal mining.

Australian Black Opal Stone – What is Black Opal?

The Australian Black Opal Stone is a non-crystalline natural gemstone that most often changes colour when rotated at different angles.

This rare and unique gemstone is a formation from the combination of silicon dioxide (silica & oxygen) with water, and ideally between 3 to 10 percent moisture content by weight. Quality solid Black Opal Stone contains 5-6 percent water.

The estimation for a 1 cm thick silica vein to form is around 5-6 million years.

For more information please click on this link → What is Black Opal?

Australian Black Opal Stone – Seams & Nobbies

The Australian Black Opal is a highly valued gemstone and can attract a price of up to US $15,000 a carat.

Black Opal Stone exists in claystone layers at depths between 20 to 60 feet below the ground surface of the Griman Creek Formation and the greyish claystone (opal dirt) lies below overlying sandstone and conglomerate rock.

Black Opal forms in horizontal deposits referred to as seams and also forms in rounded nodules of potch and colour called ‘nobbies.’

Mining Black Opal is hard yakka and the best time to prospect is in the colder months due to the extreme hot conditions during summer.

And in the earlier days, picks and shovels were the only tools available to remove rock.

Australian Black Opal Stone – Body & Soul

australian black opal stone
Transforming rough into a small cab

When an opal is cut, rubbed, shaped, and polished into a finished gemstone, it is called a cabochon. The cabochon is then made into beautiful jewelry such as pendants, bracelets, rings, and earrings. However, in some circumstances, it is best to go with the shape of the opal and not to try and do a fancy cabochon, WHY? because you can lose colour. I have been there and done that. If you do happen to have a piece that you can get a nice cab out of, then go for it. But, if youdon’t just go with the flow and shape of the stone, and retain as much colour as you possibly can. Colour is opal.

Identifying loose Solid Black Opal is easy because there are no layers. However, imitation Black Opal set in jewelry can be more difficult to recognize, and by Australian law, must be labeled as imitations. The most common known imitations are the Gilson opal (laboratory-produced), doublets, and triplets. Price should also be a guide in determining whether the opal is a solid black opal or an imitation!!! It should also be noted that Ethiopian opal is not black opal.

ALL Opals n Jewels Australian Solid Black Opals DO NOT have any materials adhered to their structure and are unaltered natural pieces of art more scarce than diamonds. We do not sell doublets, triplets or synthetic Opal. ALL Opals n Jewels opals are solid Australian Black Opal Stone.

Australian Black Opal Stone – Opal Facts

  • Australia produces approximately 95 percent of the World’s Opal
  • South Australia provides about 80 percent in the form of White Opal
  • Queensland and NSW share the remaining 15 percent
  • Queensland is known for Boulder Opal
  • The NSW town of White Cliffs is famous for the Pineapple and White Opals
  • The NSW town of Lightning Ridge is World renowned for the rare Black Opal

Australian Black Opal Stone – Australian Opal Guide

There are rogue dealers in any industry, and the jewelry industry is no exception. There are those that will falsely advertise fakes as the real deal. So if a merchant presents you with an opal, set in jewelry for under $30, the chances are it’s an imitation.

What to look out for:

  • The Country of Origin – 95 percent of the world’s opals come from Australia
  • Price – The rare Australian Black Opal is not cheap, and can attract a price of up to Aud $20,000 per carat
  • Patterns – laboratory made stones have snake-like orderly patterns.
  • Colours – large bright patches indicate an artificial opal.
  • The Depth of Colour – Colour just beneath the surface indicates a fake, depth of colour indicates a real opal (view under white light only).
  • Layers – check the sides to see if there are any layers.
  • Cloudy Stone – If you see a cloudy stone then it is most likely a doublet or a triplet (water penetrating through an adhered layer).

It would be great to hear your thoughts on Black Opal, and if you have any questions, please feel free to ask.

We have a stunning collection of beautiful solid Black Opal stone pendants and necklaces for you to choose from.

By the way, if you like opal what is your favourite colour?


brad opals n jewels






Related Links

What is black opal?
Lightning Ridge black opal
Lightning Ridge opal mining
Australian black opal pendants