In the lapidary trade, the term chalcedony is used in a limited sense, describing only the blue and white varieties, and thereby distinguisihing this gem from the kaleidoscopic variety of agate, and other forms of the entire group that is also named chalcedony. The chalcedony crystal includes a large number of types, such as chrysoprase, carnelian, jasper, bloodstone, sard, petrified wood and agate. The many sub-varieties make chalcedony, which is not a mineral species but a form of quartz, one of the biggest ‘families’ of gems. Chalcedony is most commonly translucent or light coloured with a pale glow, although, it can appear in a wide range of colours, grey, bluish-grey or even in shades from pale brown to almost black.
The Petrified Forest National Monument in Arizona, is the site of an entire forest that was transformed into petrified wood. The remains of this ancient forest can be seen in the huge silicified logs that are found here.
The name probably comes from the Greek city of Chalcedon, on the Bosphorus. The Greek word ‘chalcedony’ is mentioned in the Book of Revelation, although it is not possible to say with certainty whether it was the same mineral now known under this name. Chalcedonius the Latin form of the word, which appears in Pliny the Elder's book Naturalis Historia and refers to a specific form of jasper.
The gem has played an important role throughout history. The Jewish priest Aaron, Moses brother, was reported to have worn a breastplate with 12 stones that symbolized the 12 tribes of Israel. One of these stones is said to be chalcedony. On the other hand, the Roman orator Cicero wore blue chalcedony around his neck, believing this stone to provide the power for good public speaking. In the first century AD in Afghanistan, miscellaneous items such as seals and knives were hand-made from chalcedony. Moreover, the stone was found to be ideally suited for the seals that date from before 1800 BC because the wax does not stick to the stone. Taking their place in beautiful jewellery collections were the engraved rings of chalcedony found along the trade routes of Central Asia in a later period.
Throughout history, people have believed that chalcedony protects against phantoms and nightmares.
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