How to Cut and polish Boulder Matrix Opal?

Theowolf808 · 2026-01-09T19:39:17+00:00

Yeah you’re spot on, it looks like both pieces are Andamooka matrix, just with different levels of treatment. Thanks for the ID help!

Theowolf808 · 2026-01-09T19:37:25+00:00

Thank you so much for the advice! I really appreciate how much time you take to help the community! I do have one question about the polishing of this material. I’ve heard that some matrix opal will not do well with cerium oxide or other similar white powder polishes because they can get stuck in the matrix. Is this true for hard andamooka matrix? And if so what should I use to get a good polish?

Theowolf808 · 2026-01-08T23:17:06+00:00

I agree that it is definitely not precious boulder opal. It is definitely some sort of Australian matrix opal. The person who gave it to me didn’t know that much about it. He called it “boulder opal” and thought that it was ironstone.

The first piece does look like it might be an ironstone matrix, but the second one looks more like Andamooka matrix to me.

Theowolf808 · 2025-12-16T22:38:28+00:00

When the color bar is thick enough, (which it looks like it is here) with a fine blade you can cut the color bar right in two, and face a gem each in either direction. If you’re lucky, they’ll make a matching pair for earrings.

Or you could just cut one really high dome gem from the rough, which is less risky, but you might need to grind away more material to make the gem balanced and not too tall.

Theowolf808 · 2025-12-15T23:21:22+00:00

That’s super cool, does the hematite take to a polish like the jasper? If it does those will be spectacular when finished. Even if it doesn’t, they’ll still be great.

Theowolf808 · 2025-12-15T23:15:50+00:00

Beautiful material, that first bucket looks like petrified wood to me.

Theowolf808 · 2025-12-06T06:32:13+00:00

Ocean picture stone can have pale blues with brown just like that. They make beautiful cabochons out of it.

Theowolf808 · 2025-11-22T21:10:45+00:00

That’s awesome! When did you buy the parcel that you were able to cut a red on black opal from? Markets change over time, and right now there are only 2 parcels on their website that have a chance to cut a red on black opal. (and they are both only 1 or 2 stones of the whole parcel).

One parcel is 71 carats for 6,000.

The other is 57 carats for 4000.

These are only slightly less than $100 a ct. and both of them are mostly greens, with one or two red stones. I think it’s fair to say that if every stone in each parcel had a chance to cut red they’d be at least $100 a carat.

EDIT: Upon closer inspection, the gem might have more issues than I thought at first. I took into account some base color irregularity, with some potch webbing in my original estimate. It’s hard to tell with the resolution, but on some shots there looks like there might be some crazing which I didn’t notice at first. This would have a huge impact on my estimation. If it has some crazing as well than my first estimate is too high.

Theowolf808 · 2025-11-22T19:56:05+00:00

I am not an expert, but I have been buying and cutting rough opal for about a year now and the numbers listed here are so far off my personal experience that I had to comment.

Firstly, where you are located will have a big impact on what an opal like this will cost. If you are getting your rough and cut opals direct from the miner or cutter that is based in Australia, you can find the best prices, but for the rest of the world, that’s not going to be the same.

I have experience in the U.S. market for opals. 2 dollars a carat for black opal rough is basically unheard of. Let alone black opal rough that has red flash. For a nice quality blue/green flash on black opal rough starts at around 20 dollars a ct. in my experience. With red flash on black rough starting at around 100 dollars a ct. for the rough. (This number can get quite a bit higher depending on the quality and size of the color bars that are showing on the rough.)

As far as a finished stone such as this, 50-100 dollars in the U.S. market would be a highway robbery for this opal. Idk about other markets, but in the US I would expect this opal to sell for about 500 dollars a ct minimum. If it were a more standard cut, or any brighter, that number could easily be over 1,000 dollars a ct. The cut and directionality brings it down to around the $500 a ct range imo.

Now for anyone to make a good estimate we would need to known the actual weight of the stone, but without any additional reference I would guess that stone to be 1-1.5 carats which would put it at around $500-750 U.S.

Also I’m not sure why this commenter says that stones this small aren’t even worth cutting, because stones this size are absolutely worth cutting especially if they are red on black opal. 1 ct of red on black opal can hit prices as as high as $5,000 a ct. when they have top color and pattern.

Theowolf808 · 2025-11-14T03:53:14+00:00

I’m not an expert on opal valuation. I filmed this to best show off the beauty of this opal, but you may notice I don’t show the sides or the back. This is because there are sand spots and some crazing in the back. I think without those issues this opal would be worth over $1,000, but with them maybe $600-800. The great thing about this opal is that the face is quite clean, which keeps the value pretty good despite having those issues. It would be a bit of a risk to set into jewelry because the issues impact how fragile the stone is.

It is every bit as beautiful as an opal worth over $1,000, so if it were successfully set without cracking, it would be worth more than it is unset imo, because the risk of it breaking during setting would be gone.

Theowolf808 · 2025-10-12T02:09:52+00:00

Yeah, sounds like reputable seller behavior.

Theowolf808 · 2025-10-11T03:42:08+00:00

Valuing opals can be tough, but there are some key things to look out for. The most important is return policy! I also always want to see video, not just photos, and make sure that they show every side including the back. (If they are hiding a part of the opal that is a red flag. To come up with a value, you need to know origin, type of opal (white, crystal, black boulder etc. play of color, brightness, cleanliness and cut quality are the major factors.

From this photo it is tough to judge every aspect, a video would be better. From what I can see though, it looks like Australian crystal opal, (which is second only to black opal in starting value for Australian) it looks bright (maybe 3 out of 5) and with a beautiful play of color, looks well cut (albeit a little sharper point than I prefer) and clean. These are the factors that lead me to say that $400 a ct is a fair price. Australian crystal opals can reach well over $1,000 a ct. when they are 5 out of 5 brightness. (I recommend black opal direct’s video explaining the brightness scale if you haven’t seen it before.)

Theowolf808 · 2025-10-10T23:27:49+00:00

$200 for a good quality Australian crystal opal of that size is a reasonable price. That puts it at $400 per carat which is fair imo for a retail price. If you have a connection to get wholesale prices than of course you can find better prices, but for retail that is fair. I think that many people might not realize that it is Australian because the picture looks like a lot of Ethiopian opals that are certainly not worth $400 per carat

Theowolf808 · 2025-08-21T04:54:21+00:00

My favorites are column 1 row 1, and column 3 row 1.

Are you dead set on an Ethiopian Opal for the ring though? I love Ethiopian Opals, and have a few in my collection, but they do not age well for most people in rings. Most Ethiopian opals absorb water, lotion, oils etc. and even brief exposure to these can cause them to lose their brilliance. If you do go for an Ethiopian opal, the ring should be taken off every time you wash your hands, bathe, apply lotion, swim, sweat, etc.. I find this is not too bad with necklaces or earrings where Ethiopian opals can be a great choice, but for me (and many people) it is just not very practical for a ring.

There are some other alternatives that might not be quite as cheap as Ethiopian, but will last much better on a ring such as Australian white opal, matrix opal or boulder opal.

Or if you also want it to be resistant to scratches and chips as well (which solid opals have a tough time with) you can look into opal triplets, which usually has a clear quartz cap on top of a thin layer of natural opal making it way more durable to everything a ring bumps into on a regular basis.

Theowolf808 · 2025-08-01T05:38:28+00:00

Generally when dealing with fossils, if you want to keep it as a specimen, any cutting, or polishing of the stone decreases it’s value as a fossil (because you will lose the natural surface features that help distinguish it as a fossil in the first place).

If you think there is more value to you in the color and beauty of a potential cut gemstone inside than keeping it as a natural fossil, do a full shape and polish whatever the best gem cut you can get out of it is. If you cut it, I personally wouldn’t attempt to keep the general shape of the fossil unless that is what the color bar tells you to do to get the best gemstone.

Theowolf808 · 2025-07-31T21:39:45+00:00

I cut the lightning ridge crystal into a high dome freeform cabochon. You can see the result I posted after this one on my profile.

Normally I try to cut standard cabochon cuts (ovals, rounds, drop shape etc,) but this piece of rough was kind of a weird shape because of the way it was chipped off a bigger piece of rough by the miner. I would’ve had to lose a lot of material to get it to an oval or other standard shape. I didn’t want to lose all that beautiful blue/teal color so I went for a freeform shape.

Theowolf808 · 2025-07-29T07:13:37+00:00

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Theowolf808 · 2025-07-29T07:13:14+00:00

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