Chalcedon
The site of Chalcedon is located on a small peninsula on the north coast of the Sea of Marmara, near the mouth of the Bosphorus. A stream, called the Chalcis or Chalcedon in antiquity and now known as the Kurbağalıdere (Turkish: "stream with frogs"), flows into Fenerbahçe bay. There Greek colonists from Megara in Attica founded the settlement of Chalcedon in 685 BC, some seventeen years before Byzantium.
Chalcedony
The name "chalcedony" comes from the Latin "chalcedonius" (alternatively spelled "calchedonius"). The name appears in Pliny the Elder's "Naturalis Historia" as a term for a translucid kind of Jaspis. The name is probably derived from the town Chalcedon in Asia Minor. The Greek word "khalkedon" (χαλκηδών) also appears in the Book of Revelation (Apc 21,19). It is a hapax legomenon found nowhere else, so it is hard to tell whether the precious gem mentioned in the Bible is the same mineral known by this name today.