|Chalcedony Technically, chalcedony is any form of microcrystalline or cryptocrystalline quartz, meaning any form of quartz whose crystals are too small to be seen without high magnification. In common practice, only the translucent, single color types are sold as "chalcedony", whereas the rest of this group is sold under individual variety names, such as agate, carnelian, bloodstone, jasper or onyx. Chalcedony is named after the ancient seaport of Chalcedon (Kardikoy, Turkey).
Where is Chalcedony found?
Common Chalcedony Treatments
Chalcedony legends & lore
In the narrow sense, chalcedony will mean any translucent, cryptocrystalline quartz with a single color, whether it has a special variety name or not. Its colors are bluish, white, or gray. The various types differ in color due to metallic impurities, such as iron, nickel, copper, and titanium, present during crystallization.
Some of the best known chalcedony species are:
Agate is distinguished by having multiple colors. Banded agates are some of the most popular. A rarity is the so-called fire agate. The iridescent colors of red, gold, green and rarely, blue-violet, result from interference between light rays traveling through these thin layers. Agate jasper, which grows together with agate, is yellow, brown, or green blended. Onyx is a layered stone with a black base and a white upper layer.
Bloodstone is an opaque, dark-green chalcedony with red spots (caused by iron oxide).
Blue chalcedony, called "Mohave" and "Mt. Airy Blues", originating in California and Nevada, are slightly to moderately grayish blue with a light to medium color range. Blue chalcedony from Namibia, often called "African Blue", varies from grayish to nearly pure blue and from light to medium dark. The most unusual and most valuable type is from Oregon. Its blues are modified by slight to moderate amounts of pink, making a noticeably lavender gem, which nonetheless is called "Holly Blue."
Chalcedony, in the narrow sense, comes in bluish white or gray. Unicolored chalcedony sometimes is called onyx.
Carnelian ranges in color from yellow-orange to rich, near reddish orange, to orangey brown, and varies from semi-opaque to highly translucent. Cornelian onyx is a layered stone with a red base and a white upper layer.
Chrysoprase, apple green chalcedony that derives its color from nickel, ranges from nearly opaque to nearly transparent. Its color spectrum includes olivey, to nearly pure greens of medium tone. Very fine, highly saturated pieces have been successfully misrepresented as Imperial jade.
Chrysocolla Chalcedony, marketed as "Gem Silica" this relatively rare, blue to blue-green, opaque to near transparent material is the most expensive type of chalcedony. Its color agent is copper.
Like at any other gemstone the saturation of color defines quality and value.
Chalcedony is typically translucent to opaque, with a waxy or dull luster.
Chalcedony is usually cut as cabochon or carved, although an exceptional, near transparent piece may be faceted.
Chalcedony location and deposits
Australia: Agate, chrysoprase, bloodstone
Brazil: Agate, chalcedony, bloodstone, chrysoprase
China: Agate, bloodstone
India: Agate, chalcedony, bloodstone, carnelian, chrysoprase
Madagascar: Agate, chalcedony, chrysoprase
Namibia: Agate, blue chalcedony, chalcedony,
Sri Lanka: Chalcedony,
Uruguay: Agate, chalcedony,
South Africa: Chrysoprase
Zimbabwe: Chalcedony, chrysoprase
USA: Agate (Montana and Wyoming), chalcedony (California), chrysocolla chalcedony (Arizona), bloodstone, blue chalcedony (California, Nevada, Oregon)
Common Chalcedony treatments
Carnelian is regularly heated to darken the red tones. Banded agates are dyed to revitalize the colors.
Color: Bluish, white, gray
Chemical composition: SiO, silicon dioxide
Crystal system: (Trigonal) fibrous aggregates
Hardness: 6.5 - 7 (Mohs scale)
Specific gravity: 2.58 - 2.64
Refractive index: 1.530 - 1.540
Birefringence: up to 0.004
Color of streak: White
Absorption spectrum: dyed blue: 690 - 660
The Chalcedony zodiac, myth & legend
Archaeologists have dug up Babylonian and Assyrian cylinder-seals carved out of chalcedony dating from 500BC. Onyx is the birthstone for those who are born in December. In the Zodiac chart, Onyx is the stone for Leo and Carnelian for Virgo.
In Antiquity, as well as in the Middle Ages people believed that the cosmos is reflected in gemstones. The Carnelian is assigned to planet Neptune. The esoteric movement revived the ancient belief and the gem industry made it another marketing tool to promote certain gems.
The healing powers of gems remain a controversial issue, but are mentioned for centuries by healers, shamans and medicine men. Whether its factual or a placebo effect doesn't matter, if it helps. The safest approach is to wear the gemstone in skin contact to the troubled part of the body. Carnelian, as well as chalcedony, is said to be of help for heart ailments. Agate is said to support the healing of blisters.