jasper

jasper, opaque, fine-grained or dense variety of the silica mineral chert that exhibits various colours. Chiefly brick red to brownish red, it owes its colour to admixed hematite; but when it occurs with clay admixed, the colour is a yellowish white or gray, or with goethite a brown or yellow. Jasper, long used for jewelry and ornamentation, has a dull lustre but takes a fine polish; its hardness and other physical properties are those of...