Agate is a quartz silica mineral. It consists of successive layers of chalcedony, each of which has a different color. An incision into agate will reveal thin parallel curved lines of chalcedony. It took its name from the Achates river in Sicily (nowadays called Dirillo) where it was first found. It is a very common mineral and is encountered in almost every color. It is usually opaque. In the Bible it is identified with the eighth tribe of Israel, the tribe of Levi. It is mined in Brazil, Uruguay, Germany, and Italy.