Opal Var. BOULDER Opal in IRONSTONE

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A stunning specimen of the Opal variety known as 'Boulder Opal' from one of the less well-known Australian opal localities of Quilpie in southern Queensland, Australia. The siliceous ironstone matrix varies from milk chocolate to dark chocolate-brown and is part of a larger concretion which has fractured internally at some stage of its formation, similar to a septarian nodule. In this case, the fracture filling has been a colloidal silicate gel leading to the formation of Opal. The specimen has been sawn to form a base and is highly polished on all faces. The display face is a spectacular network of polygonal facture infillings of electric blue and green Opal with a major opalized area of approximately 6.5 x 4 cm. The Opal is predominantly vivid shades of blue, mauve, violet and green, but shows occasional bright flashes of orange-red. A thoroughly excellent example of 'Boulder Opal' from Queensland and of high-end museum quality.