In this field demonstration, Paul Edgren explains the geology, value, and cutting process of Yowah ironstone (boulder) opal in Queensland, Australia. He describes how ironstone, a sedimentary rock with about 5% iron, forms as nodules that flatten over time, creating voids that later fill with silica‑laden water from the Great Artesian Basin, producing opal spheres that display vivid colors. These opal‑filled concretions, called "nuts," can be worth $10,000‑$25,000 if they contain a crystal center. To extract the opal without damaging it, Paul uses a high‑speed diamond saw running at over 6,000 RPM, with abundant water cooling to keep the blade clean and reduce heat. He emphasizes safety—keeping fingers away from the blade—and notes that the water used is hot, naturally heated by the earth, sourced from a 1,700‑foot‑deep bore delivering about 200,000 gallons per day. The segment also includes a brief field report: after an hour of collecting nuts, they spent half an hour cutting and found a small piece of green speckled opal.
Chapters
What I'm cutting here is ironstone opal. Ironstone is actually a stone that, assayed out, will be about 5% iron. It's extremely hard, and it's in the— lays in a lens in the bottom of ancient seabed at sometimes levels as deep as 50 feet here in Yawa. It's also referred to as boulder opal, but not to be confused with a volcanic opal. It's actually a sedimentary opal. And wherein this ironstone formed as possibly round nodules, and then with time and weight flattened out much like a flattened pancake. And so in— when this process took place, it caused voids in the ironstone. Silica-laden water percolated either through it from the ground, through the sandstone, or up from the bottom, since this is the Great Artesian Basin and mineral water comes up through it. In any event, these voids filled with silica-laden water and laid down opal, you might say, or basically silica, perfect spheres of silica that threw off on the reflection of light beautiful colors of blue, green, red, and yellow. And so what we're doing here is we're actually sawing these concretions in half, and you may have to many times saw hundreds or even thousands of them until you find one that either would have the small opal pieces in the matrix, they call it, in the middle, or even a crystal center. If you found a really valuable, what we call a nut here in Yawa, you could have a value of $10,000 to possibly even $25,000. So it makes it worth your while to cut every one rather than hitting it with a hammer, because if you hit it with a hammer to see if there's opal in the center, you would very many times fracture the opal and greatly decrease its value. It's a diamond saw. Most diamond saws run about 3,000 RPMs, but here in the opal fields, we run these at double that, over 6,000 RPMs, and we use a large amount of water as we've got to keep the diamond blade extremely clean. And so, uh, that's what we do. It's a pretty quick process. You do have to be careful because you don't want to put your fingers in the diamond saw, but it's not quite as dangerous as a as a wood saw might be, but you still wouldn't want to do it.
So it's, um, moving quickly because we've got it on double speed. We spent about, what, an hour out collecting some nuts this morning, and then this afternoon about half an hour cutting them. And did we find any opal today?
Uh, one small piece.
That's true, we did. A little bit of green, green speckles. The water comes out of the ground hot here, which is really interesting. It comes out of those little nodules straight onto the blade, and it's nice warm water. You turn the hot shower tap on and it's coming straight out of the ground. It's not, um, not heated up anywhere. It's heated up by the earth.
The well, or bore as you refer to it here, is over 1,700 feet deep and was drilled in the early 1900s and runs about 200,000 gallons a day.
Wow. Well, thanks, Dad, so much for showing us this. We've been out here in Yowa a few times over the last couple decades, and this was a special time because we brought Mikey. Say hi, Mike. Hi. And that is all we have.
