Solid Australian Black Opal
Untreated black opal is hard to find these days but this one, from Australia, is a good example of what Black opal should look like. Its play-of-color is mostly greenish-blue, the free-form cabochon is 3.01 cts. in weight and it measures 15.42 mm x 6.7 mm x 4.8 mm. This stone would make a beautiful pendant, and we would be happy to design one specifically for you.
Hardness and toughness
Opal hardness is variable depending on its exact composition and formation conditions, and ranges from 5 to 6.5 on the Mohs scale. Its toughness is very poor to fair, making opal a gem that is suitable for jewelry but requires care when wearing so as to not scratch or break the stone.
Opal is generally stable, but heat from intense light can cause fracture lines called “crazing.” High heat or sudden temperature changes can also cause opal to fracture. Opal is attacked by hydrofluoric acid and caustic alkaline solutions.
The only safe way to clean opal is with warm, soapy water.