Information about Chalcedony

Chalcedony consists of cryptocrystalline silica – very fine intergrowths of quartz and moganite.

Many well known minerals are forms of chalcedony of one form or another – Agate, Carnelian, Chrysoprase, Heliotrope, and Onyx are all forms of chalcedony.

Uses and History

Chalcedony has been worked since antiquity, with a great amount of archaeological evidence of its use by the ancient Egyptians, Greeks, and Romans.

Sites in central Australia show the material was used for making knives or other bladed tools as much as 32000 years ago.

It was widely used as a decorative stone, too – cameos and carvings from ancient Crete, Rome, and Greece are well known and famous.

It is still widely used in jewellery today, with cabochons and beads being very well known. Other lapidary items are made from chalcedony too – eggs, spheres, pyramids and other carvings are very popular/

Chalcedony was named after the Latin word chalcedonius, probably named after the Greek city of Chalcedon, which is now the current day Turkish city of Kadıköy.

Mineralogy

Hazards and Warnings

Typically safe to handle, but silica dust is toxic to humans.

Mineral collectors should wash their hands after handling specimens, to avoid any exposure to potential toxins.

Almost all rocks, minerals (and, frankly, almost all other substances on earth) can produce toxic dust when cutting, which can cause serious respiratory conditions including silicosis.

When cutting or polishing rocks, minerals, shells, etc, all work should be done wet to minimise the dust, and a suitable respirator or extraction system should be used.

Translations

Further Reading / External Links

• https://www.mindat.org/min-960.html
• https://en.wikipedia.org/wiki/Chalcedony
• https://www.minerals.net/gemstone/chalcedony_gemstone.aspx
• https://www.minerals.net/mineral/chalcedony.aspx