Chalcedony

Chalcedony (Greek chalkêdôn) appears in Scripture only in Revelation 21:19 as the third stone in the twelve foundations of the wall of the New Jerusalem. The name derives from the ancient city of Chalcedon on the Bosphorus. In modern mineralogy chalcedony refers to a microcrystalline form of quartz that comes in many varieties — including agate, carnelian, and jasper — but the ancient term is of uncertain application; John's intended stone may have been a blue or sky-blue variety, an emerald-green stone, or copper ore. Some identify it with the modern turquoise. The stone appears among those associated with the breastplate of the high priest in Ezekiel 28:13 (in forms rendered differently in ancient versions).