Boulder OpalsFine grade boulder opals have the top surface covered with precious opal. Slight marks and protrusions of ironstone in the face of the stone are fairly typical, and can affect value. Boulder opal is usually cut to the contours of the opal vein creating a baroque wavy surface and they are often irregular in shape. The most expensive boulder opals are those with a dark body tone and displaying a full face of brilliant precious opal.
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