24 January 2012

World's largest opal matrix (55,000 carats)

"The opal is about 30 cms in length with a height of 15-20 cms and a 4 cm thickness. Its estimated value is at least 1 million dollars USD... Historically, the largest opal found so far was just 6,100 carats in size. The current one is nearly ten times that size."
Photo and text via JustLuxe.  I often see opals at rock and mineral shows, but have never owned one or understood their geology, so I had to look up the details -
Matrix opals are a type of boulder opal and are found as part of a host rock, called Boulder ironstone.  They contain opal randomly distributed through the rock. The boulder ironstone with the precious opal inclusions are cut as one piece, giving an appearance similar to what you see when you look at the night sky, except that the ‘stars’ in this case are flecks of glories opal color.

Different types of matrix opals come from a variety of fields.  Boulder matrix comes from the Queensland fields in the northern part of the opal regions in Australia. There is another form of matrix opal from Andamooka in South Australia which is treated to give it a darker background. The specimen is soaked in sugar solution and boiled in acid, which causes carbon to get deposited in the spaces in the rock, giving it a dark or black opal appearance.
From Opalmine, which has pix of examples for sale.  Rock and mineral collecting has changed a lot since I was a kid in the 50s; nowadays much of what is available for purchase has been altered chemically or with heat or with radiation.  But with worldwide transportation much improved, there are now some amazing finds and products available.

Via the newsletter of the Madison Gem and Mineral Club.


  1. If I remember (more than a decade) when I was in the jewelry business, matrix opal was was often some cheap stuff that if treated correctly produced beautiful gems. It was white with flashes of color but the whiteness of the base did not show the colors well and came off pretty bland. The treatment was to simmer the matrix opal in a concentrated sugar solution for a set period of time and then put the simmered opal into a solution (i don't recall the concentration) of sulfuric acid. This carbonized the sugar which had infiltrated the matrix and turned the opal black. This showed off the colors much better.

    This may be the case here since while it is an impressive piece just average quality black opal can cost $300 a carat and top quality can run more than $5,000 a carat. Gemstones will almost always have a size premium, i.e. large sizes of inferior quality can cost more per carat than higher quality small sizes.

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  3. "Here Honey, I hope you like your new ring. Oops! Didn't mean to crush your hand!"

  4. The "gentleman" who found this has a rather colourful history...


    Buyer beware!

    1. Interesting. I wasn't sure it was the same guy, but tracked down this article which references both computers and the opal (and many other things) -


    2. To pads and Minnesotastan. Just to put the record straight I am actually the owner of this opal matrix specimen.I was given Stuart Hughes name by a friend of mine in Australia. Stuart has been nothing but straight up with me. He found a group who are interested in buying it, which I would never have been able to do. He passed the buyers details to me without asking for any upfront payment etc.
      If anyone wants any details about this specimen i would be glad to answer any questions

    3. matrixopal didn't leave an email, so readers are welcome to ask questions via this comment thread.

  5. I'm not so sure about the "record" part of this opal. I "can" say that in the 70's my partner and I treated pounds and pounds of Andamooka matrix in smaller sizes (up to maybe 10 oz chunks). The largest specimen piece, if I remember correctly, was around 15,000 cts. We displayed it in a 10 gal. aquarium full of water. We never treated it. I remember it being fairly rich in silica and would have been absolutely georgeous treated. $10,000 would have bought it from us in those days. I would like to personally see this specimen shown above to satisfy my curiosity of it being Andamooka. It doesn't look like Queensland Boulder---if not Andamooka then it looks maybe like Honduran. For sure, Andamooka doesn't look like this untill it's treated and polished.

  6. That's not the biggest rainbow matrix from Andamooka and the best way to treat the stone in in sugar then wrapt in alfoil then put on hot Coles no flames to turn the sugar to carbon and the background of the stone black.


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