Sardius
SARDIUS, SARDIN, SARD sär’ dĭ əs, sär din, särd, a translucent variety of very fine-grained silica (silicon dioxide). It is a subvariety of chalcedony (q.v.), brown to orange-brown by reflected light but deep red by transmitted light and sometimes referred to as a variety of carnelian (q.v.) (cf. KJV and NEB Rev 21:20). It is a semi-precious stone (Exod 28:17).