Chalcedon
Chalcedon ( or ;
, sometimes transliterated as "Chalkedon") was an ancient maritime town of Bithynia, in Asia Minor. It was located almost directly opposite Byzantium, south of Scutari (modern Üsküdar) and it is now a district of the city of Istanbul named Kadıköy. The name "Chalcedon" is a variant of Calchedon, found on all the coins of the town as well as in manuscripts of Herodotus's "Histories", Xenophon's "Hellenica", Arrian's "Anabasis", and other works. Except for a tower, almost no above-ground vestiges of the ancient city survive in Kadıköy today; artifacts uncovered at Altıyol and other excavation sites are on display at the Istanbul Archaeological Museum.
Chalcedony
In the 19th century, Idar-Oberstein, Germany, became the world's largest chalcedony processing center, working mostly on agates. Most of these agates were from Latin America, in particular Brazil. Originally the agate carving industry around Idar and Oberstein was driven by local deposits that were mined in the 15th century. Several factors contributed to the re-emergence of Idar-Oberstein as agate center of the world: ships brought agate nodules back as ballast, thus providing extremely cheap transport. In addition, cheap labor and a superior knowledge of chemistry allowed them to dye the agates in any color with processes that were kept secret. Each mill in Idar-Oberstein had four or five grindstones. These were of red sandstone, obtained from Zweibrücken; and two men ordinarily worked together at the same stone.