Agate

Hebrew kadkod, from kadad, "to sparkle". The "windows" being of this gem (Isaiah 54:12) implies transparency. Gesenius thinks the ruby or carbuncle is meant. It was imported from Syria to Tyre (Ezekiel 27:16). Hebrew Sheba (from Sheba whence it came to Tyre), Exodus 28:19; Exodus 39:12, is rightly translated "agate," a semi-transparent uncrystallized quartz, mainly silica, with concentric layers of various tints; the second stone of the third row on the high priest's breast-plate. The English term is drawn from that of the Greeks, who found agate in the river Acheres, in Sicily, and hence named it.