Chalcedony was not used in the High Priest's breastplate (Exodus 28:17 - 20). It was also not one of the many gemstones used to adorn Lucifer (Ezekiel 28:13). Eight of the ten Bible versions referenced in this series translate this stone as "chalcedony." The ESV and NLT translations refer to this stone as an "agate."
The name of the stone comes from the ancient city of Chalcedon, located in the Roman province of Bithynia, from where it is believed it was first discovered.
More than seventy varieties of this gemstone are known to exist, including agates, bloodstones, carnelians, chrysoprases, flints, onyxes, jaspers and others. These gemstones are a variety of quartz that generally appears to have a waxy luster. The most common colors found in the stone include variations of white, gray, reddish or light brown, green and blue.
According to a U.S. Geological Survey article on Chalcedony, because of the stone's abundance and durability it was one of the earliest raw materials used by man. The first recorded uses of this stone were for projectile points (e.g. spears), cutting edges of knives and for fashioning bowls and cups.
An amulet with a carbuncle and a chalcedony gemstone in it was believed to protect sailors from drowning. This stone was also thought to drive away "phantoms" (ghosts) and night visions by dissipating the "evil humors" of the eyes, thus removing any disease which existed and stopping the apparitions (Curious Lore of Precious Stones, page 39, 65).