Sardonyx
SARDONYX sär’ də nĭks, a semi-precious (Rev 21:20) variety of chalcedony (q.v.) which is very fine-grained silica (silicon dioxide). Like agate (q.v.) it consists of layers of different colors, in this case white or bluish-white and red, or brownish-red, but the layers are in even planes and the banding straight.