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Roger Weller, geology instructor                                       

wellerr@cochise.edu
Quartz Family Gemstones-by Audrey LaClair
                            
                          Chalcedony
 

Chalcedony, also spelled Calcedony, is a term that includes many well known cryptocrystalline quartz gemstones.  It has a waxy luster and is found in all of the 50 states, which include different colors, and in sedimentary, igneous, and metamorphic rocks.  “Chalcedony includes carnelian, sard, plasma, prase, bloodstone, onyx, sardonyx, chrysoprase, thundereggs, agate, flint, chert, jasper, petrified wood, and petrified dinosaur bone just to name a few of the better known varieties”

(http://minerals.usgs.gov/minerals/pubs/commodity/gemstones/sp14-95/chalcedony.html).
 

photo by R.Weller
 

“Chalcedony is a very fine-grained (cryptocrystalline) variety of the silica mineral quartz.  A form of chert, it forms rounded crusts, rinds or stalactites (mineral deposits suspended from the roofs of caverns) in volcanic and sedimentary. It has a compact fibrous

structure and fine splintery fracture” (http://www.desertusa.com/mag99/june/papr/chalcedony.html).  You can find other physical properties of quartz vividly colored in the petrified forests in the southwestern deserts.  Chalcedony has replaced many of the original tree tissues in the formation of petrified wood.  Iron oxide is primarily what causes the beautiful greens and reds.  You can find some of the best petrified wood in eastern Arizona’s Petrified Forest National Park.

photo by R.Weller

Chalcedony has been used as gems in all ages, and many beautifully colored varieties are still cut and polished to this day.  Although, Chalcedony is much less valued than what it once way.  Uruguay, Brazil and southwestern Africa primarily produces it

commercially.   “It is said that chalcedony was used as a sacred stone by the Native Americas, promoting stability within the ceremonial activities of the tribe. Chalcedony is said to augment emotional balance, vitality, stamina, endurance, kindness, charity and friendliness. It supposedly alleviates hostilities, irritability and melancholy”

(http://www.desertusa.com/mag99/june/papr/chalcedony.html).

References
 

http://www.desertusa.com/mag99/june/papr/chalcedony.html

http://minerals.usgs.gov/minerals/pubs/commodity/gemstones/sp14-95/chalcedony.html