Value of Exceptional (to me) Boulder Opals

I have had the luck of purchasing a few truly exceptional Koroit bolder opals with little matrix inclusions. Here is an example. I am not sure I have seen any quite like these, but I’m guessing that doesn’t factor much in price. I don’t plan to sell, I will try and mount and give to friends as gifts, but I am curious what if such stones are valued, and if so, what might they be worth, roughly.

Also, how do the prices of single color translucent opals compare with multi-colored opaque stones? Are these valued (example below)?

Sorry, but to me it looks the top one is worth a dollar or two. It’s got maybe 10% color area and that’s a low-value blue green. If there’s more color someplace else in the stone, then it still wouldn’t be worth much as the color extinguishes when view from above.
The bottom one could be anything: opal, quarts, topaz. In any event, it’s small and included. If it’s opal, then there’s no color: potch.


Thanks. I guess taste is subjective, at some point, someone dug this up, worked it, polished it, and sold it. Who knows how many hands it’s past through, my source got it from workers digging by hand through alluvial deposits; like me, he thought it was beautiful. It would be quite a deal to buy roughly 8 carats of Koroit boulder opal for a buck, even rough and steamrolled and hacked up with a chisel. I appreciate the reply, but I am curious why this one would be so below even the lowest going fair market value for these stones. Maybe you are right, I truly don’t know, which is why I asked, and the stuff I like is regularly not the stuff that commands the highest prices, but it seems unlikely it’s essentially worthless (which is about the notional value of a stone selling for a buck)?

My takeaway is if I were to sell, it’s probably not a good idea to offer free shipping :slight_smile:

What determines opal value is color. Everything else is secondary. Reds, purples, yellows and deep blue are the desired ones - mostly in combination. The upper one has a little color but not a valuable one. Boulder opal evaluation also considers the amount of the face that displays colors as opposed that containing matrix. Value also involves size. Based on holding the stones in forceps, it’s small - maybe a carat.
So, if you had mined and polished it yourself it might have sentimental value. There are dozens of places that sell boulder that displays real color.

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Thanks. It was probably not a good question to post, the photos do not do the play of color throughout the stone justice, which varies across the stone, but is at least as rich as any other opal i’ve seen, even within the transparent sections there are unambiguous blues, yellows and various other hues).

I just re-weighed to make sure at least I got that part right. I didn’t, it’s 8.3ct.

I appreciate the reply, I was trying to be a little funny with “free shipping” comment, I hope that didn’t read as smarmy; it was not my intent.


Hi Paul. I careful looked at your photos and to help you in your future Opal collections, I would like to share what the guidelines for buying good Boulder Opals are:

" Boulder and Matrix Opals

Boulder opals have their own value structure. However, the basic ingredients of color, directionality, cut, and imperfections apply to these gems as well. In addition, the percentage amount of precious opal in the matrix affects the value of the gem. For example, a Yowah nut with 50% of the surface covered in precious opal is far more valuable than one with just 20% coverage.

The pattern created by the intermixing of the matrix and opal also affects value. Higher values go to the more interesting patterns."

I have been lucky to have purchased a Yowah nut that had excellent opal. I made it into a protective necklace to keep it from being damaged when wearing.

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Thank you for the additional information, it was super helpful. I really love these stone, I have a few more and they just draw me in for some reason. I had no idea that “nut” stones like those in the link exist, they kind of remind me of “dragon eggs” (I think they are called), which I believe are some sort of agate inside a spherical matrix. I can imagine how cutting a polishing a slice of them could look really great.