The modern stone bearing this name is a transparent or translucent cryptocrystalline variety of quartz used for ornaments and gems. It is not quite as hard as pure quartz, and it occurs in masses in the cavities of volcanic rocks. The common kind of chalcedony is partially transparent and figured with milky-white swirls and spots. It appears in many colors, such as white, gray, yellow, blue, and brown.
Chalcedony was a stone commonly used for engraved gems in ancient times. It was named after an old Greek city called Chalcedon (in Asia Minor), which once was a source of the mineral. The only Biblical text referring to this stone states that the third foundation of New Jerusalem’s wall was chalcedony (Gr., khal·ke·donʹ).—Re 21:2, 19; see JEWELS AND PRECIOUS STONES.