Koroit boulder opal is found in Paroo Shire in southwest Queensland, Australia. The opal is found in a sandstone matrix called the Winton Formation, which contains ironstone concretions. The opal forms within the layers in the sandstone and as kernals in the concretions. The brown and red banding of the sandstone combined with the multi-colored precious opal make this a stunning material for cabochons. Boulder opal with its combination of sandstone, ironstone and opal, has different hardnesses throughout the stone. Because of this, the material may be stabilized or backed. I have made boulder opal cabochons without stabilization, but you must use care when shaping as the ironstone is much harder than the sandstone or the opal.
Please enlarge and view the photographs for more detailed views. Shown wet to simulate polish. As with all natural rock, there may be fractures or pits to seal or work around. Each slab has the approximate dimensions listed. I use the longest and widest point and the thinnest, it’s not averaged.
We have worked hard with the lighting and the settings on the camera so that the colors are very accurate. Individual settings may affect color viewing on various devices and I cannot predict what your device will do, but on my computer, they’re dead on for color. I appreciate your business!