Bloodstone from The Image

Chalcedony is the cryptocrystalline variety of quartz, SiO2, and includes carnelian, sard, aventurine, onyx, sardonyx, bloodstone, chrysoprase, agate, jasper, and petrified wood and bone. Carnelian and sard are red to brown, translucent chalcedony. Aventurine chalcedony is clear quartz with green fuchite mica creating an overall green color and sparkle.

Agate from Gem Hut

Sardonyx from The Image

Onyx is black and white, and sardonyx is orange and brown varieties with straight banding. They are often carved into cameos or intaglios. Bloodstone, known as heliotrope or plasma, is green chalcedony with orange or red iron oxide inclusions. Chrysophrase is a translucent green variety of chalcedony colored by nickel.

Onyx from The Image

Agate from The Image

Agate has curved banding, with trade names such as Blue Lace, Botswana, Crazy Lace, Dendritic, Moss, and Fire Agate. Jasper, flint, and chert are all names used for granular quartz. Jasper is usually red, brown, or green and sometimes have streaks of color that look like landscapes, termed picture jasper. Flint and chert were used for projectile points, axe heads, tools, and more, by early humankind.

Picture Jasper from The Image

Moss Agate from The Image

The hardness is 7 and specific gravity 2.65. Quartz has no cleavage and conchoidal fracture. It is tough and compact, and most often fashioned in the cabochon cut. Chalcedony has a wide geographic occurrence. Agate is formed in nodular cavities associated with volcanic lavas. Agate is porous, and is therefore dyed or stained. For more information on chalcedony, visit Desert Environment and Sandra Smith's chalcedony.

Fire Agate from The Image

References

• Gem Hut (1995-2000). http://www.gemhut.com/
• International Colored Gemstone Association (1999). http://www.gemstone.org/index.html
• Mineral and Gemstone Kingdom (1997-2000). http://www.minerals.net/index.htm
• Smith, S. (June 1, 2000). Chalcedony. http://www.suite101.com/article.cfm/gems_and_minerals/40360
• The Desert Environment (1996-2000). http://www.desertusa.com/mag99/june/papr/chalcedony.html
• The Image (November 15, 2000). http://www.theimage.com/index.html

Return to the Syllabus or choose another gemstone below.

Alexan drite	Amber	Amethyst	Chalcedony	Diamond	Emerald
Garnet	Jade	Malachite	Opal	Pearl	Peridot
Ruby	Sapphire	Tanzanite	Topaz	Tourmaline	Turquoise

This page originates from the Earth Science department for the use and benefit of students enrolled at Emporia State University. For more information contact the course instructor, S. W. Aber, e-mail: saber@emporia.edu Thanks for visiting! Webpage created: November 15, 2000; last update: January 7, 2007.