I've found Madagascar Yellow Opal a challenging stone to facet. It's soft so it's very brittle. Chipping a girdle can be done with ease. It's also sensitive to heat. On removal from the dop it can chip or break also. But I will continue to learn to cut such stones as they not often faceted. Being not entirely clear, more a semi translucent stone makes it also challenging find clean clear pieces without veils, cloudiness or inclusions. But I won't let all these difficulties get the better of me. I'm determined to someday cut a nice yellow opal. Hopefully it will come from this 147 carat piece shown in this photo. Anything over 4 carats I would consider to be a large cut, considering Opal is a lighter gem in density.
I have a vein of very similar material hidden away in the bush I found while prospecting for gold, it does chip very easily I have faceted a bit just for the hell of it and tumbled some others. The vein I have found runs for about 35 metres on the surface, colour ranges from lemon yellow and is very clean through Apple green which is also clean, it then runs into a very rich chrome green with dendrites or what may be iron and clouds of possibly feldspar, pretty stuff though but very soft and brittle as you mentioned.
The green makes for a interesting colour. I'm thinking of cutting a square also. Well done on cutting this.
