Chalcedony enters English through the Bible — specifically from Revelation 21:19, where it appears as one of the twelve precious stones adorning the foundations of the heavenly Jerusalem. The word comes from Latin chalcedonius, from Greek khalkēdōn. The traditional association is with the ancient city of Chalcedon (Khalkēdōn), located on the Asian shore of the Bosphorus opposite Byzantium — modern Kadıköy, now a district of Istanbul.
However, the connection between the stone and the city is less certain than it appears. The city name Chalcedon may derive from a pre-Greek Anatolian language, and the precise relationship between the place and the mineral has never been conclusively established. Some scholars suggest the stone was traded through Chalcedon rather than mined there. Others have
Mineralogically, chalcedony is a cryptocrystalline form of silica (SiO₂), composed of extremely fine intergrowths of quartz and moganite. What makes chalcedony particularly interesting is that it is a family name rather than a specific stone. Many well-known gemstones are actually varieties of chalcedony: carnelian (red-orange), chrysoprase (green), onyx (banded black and white), agate (banded or patterned), jasper (opaque, various colors), bloodstone (dark green with red spots), and sardonyx (banded red and white). The differences between
The city of Chalcedon achieved its greatest historical significance in 451 CE, when the Fourth Ecumenical Council convened there. The Council of Chalcedon defined the Chalcedonian Definition — the doctrine that Christ possesses two natures, divine and human, united in one person. This theological formulation remains the orthodox position of the Catholic, Eastern Orthodox, and most Protestant churches. Churches that rejected the Chalcedonian Definition (the Oriental Orthodox churches of Egypt, Ethiopia, Armenia, and Syria) were labeled "non-Chalcedonian," and the resulting schism persists to this day