jasper

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jasper A variety of chalcedonic (see CHALCEDONY) Silica (SiO2) which is reddish-brown, opaque, and cryptocrystalline. It may be banded to give ‘Egyptian jasper’ (‘ribbon jasper’). A contact metamorphosed (see THERMAL METAMORPHISM) shale may also be baked to give ‘porcelain jasper’ which may be similar in appearance but has a different composition.

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