New Koroit Opal

That's sweet!

Beautiful cab, Rick. I agree with you on the patterns. If the pattern is great, the opal is just icing on the cake.

Well, sort of.... There are several different types of boulder opal and it can be one of the brightest and most valuable opals from Oz. But there's also a strong appreciation that seems to be growing in recent years for the not-so-colorful stones that have intricate and unusual patterns from the Koroit locality, as shown in my stone. I lost a bit of color in cutting it, in fact, because the pattern seemed more pleasing to me.

There's one vividly-colored type that yields incredibly beautiful gems called Churchwindows. They actually resemble stained-glass windows in churches and cathedrals with the light shining through them. Another type features thin layers of amazingly bright and valuable opal on very dark brown or blackish ironstone. Many Koroit types have spiderweb networks of very bright multicolored opal interwoven through the dark ironstone. Yowah "nuts" are ironstone concretions that have "kernels' of blindingly-bright and beautiful opal in thrilling patterns.

I could write a book. In fact, many others have. One that gives a general over-view of most types of opal and localities, with great pictures, is  "Opal: The Phenomenal Gemstone" published by Lithographie LLC, East Hampton CT. It's a luxury paperback and expensive for a paperback but worth it if you're an opal fanatic like me.

ETA: I kind of overlooked your question about cutting. My experience with cutting boulder types is "anything that works!" Each type presents different challenges --whether with shaping or trimming or polishing -- and flexibility is needed to meet them. And a warning: when cutting ironstone opals, plan on ending up with your clothes and skin stained bright red. They're ultra-messy.

Interesting info gemfeller I do know the ones I have are Koroit. They weren’t cheap. One may have to be a learning project. Hopefully I don’t screw them up. They do have great colors and patterns showing. I’m actually not much of an opal person in general, but these koroit and boulder ones, I just love the colors running through the matrix.

They're really not hard to cut but... The trick with Koroit and ironstsone boulder in general, is being able to judge the hardness of the matrix. Some is so soft it comes off on the wheels like butter. That's usually the light-colored tans. In general, the darker, the better the polish. Some takes a brilliant polish. However when light and dark are blended in the same stone, undercutting can be a serious issue.

gemfeller hummingbirdstones Thanks for the info about the light and dark matrix. That’s good to know. I will dig them out and take a look at the coloring and post some pics.

jasoninsd The Koroit cab you posted in your recent thread is a knock-out. It beats mine all to heck, especially in coloration. It seems to me you know how to cut this material. The current piece does present some challenges. It's hard to tell for sure from your images but it may be that you're stuck with a curved-bottom stone if I'm reading the pictures right. I'm assuming the part with the lovely patterns is the flattest surface. The tragedy with this material is that to cut it you often have to sacrifice some beauty. Deciding what to cut away and what to keep can cause a lot of distress. I have a piece of rough that's gem quality. But....deciding how to slab it gives me nightmares. I'll try to get pictures of it soon and post them to show my dilemma. If I get it right the result will be crackers as my Aussie friends say.

jasoninsd I wasn't suggesting you were being coy. I was trying to buck up your confidence. I started out cutting opal many years ago. I was poor. I remember waiting anxiously 3 months for 1 ounce of rough from Oz because it was shipped by sea mail and I couldn't afford air postage. I've been through many twists and turns with the lovely stuff since. I've experienced the same feelings you're going through many times. And still!

Here are some images of the frustrating piece of Koroit rough I mentioned earlier in the thread. I think I've finally come up with a slabbing strategy but I'm almost afraid to try it for fear of messing up an irreplaceable natural creation. But that's opal cutting!

Side View


Long Top View


Close Top View