Chalcedony is a fine-grained variety of quartz with crystals too small to be seen with the naked eye.
Some historical references claim chalcedony was once believed to offer protection against poisoning.
Blue chalcedony, particularly material used for gemstones, is often dyed.
Chalcedony seals dating to approximately 1800 BC have been found at the Palace of Knossos, a Bronze Age site in Crete.
Jasper, agate, carnelian, onyx, chrysoprase and bloodstone are all varieties of chalcedony.
CARNELIAN
