Chalcedony takes its name from Chalkedon, a former city in the ancient country of Bithynia.
An accumulation of microscopic quartz crystals, it is gray to blue to pale yellow in color in its purest form.
However, the presence of iron or nickel can alter its hue and its name: bright green chalcedony is called chrysoprase, red-orange chalcedony is known as cornelian, brown chalcedony is known as sard, agate is patterned chalcedony, onyx is black or black and white chalcedony, while jasper is chalcedony whose impurities give mixed shades, rendering it opaque.
Chalcedony is one of the largest families of the mineral realm.
Already popular in ancient times, its porosity means it readily absorbs stains.
Indeed, most chalcedonies on the market today are dyed, in which case they are known as blue agate, green agate, etc.
Natural or tinted, chalcedony has always been used for glyptics and is often chosen to sculpt cameos. Art Nouveau in particular brought this stone to the fore.Hardness: 6.5. Birthstone of Sagittarius. Uruguay, Brazil, India, Madagascar, United States, Czech Republic.