Cochise College           Student Papers in Geology

Geology Home Page                   physical geology  historical geology  planetary  gems           

Roger Weller, geology instructor

wellerr@cochise.edu


Black Hills, Arizona
by Necole Michael
Physical Geology
Fall 2007
         

Black Hills Rock Hounding Area

Fire Agates 

 

What is Rock Hounding?

 

Rock hounding is defined as the recreational collection of minerals and rocks found in a natural environment. Early rock hounders were known as small children or sons, who were intent on ruining their mothers wash borders. Later these rock hounders became know as prospectors. The main goal of a prospector was to look for minerals or gem stones for economical gain.


          While you do not need to be a geologist to enjoy rock hounding it is recommended that you gain a basic understanding for rocks and minerals before you being any rock hounding excursion. This will help you to identify and examine your treasures with more clarity. Rock hounding groups, internet searches and even a geology class can help you to gain the necessary knowledge to identify the classify rocks and minerals.
 

Today many areas offer the rock hounder the opportunity to explore and examine nature’s beauty. The Black Hills Rock Hounding Area in Safford Arizona is one of the many sites that allow you to obtain samples for your collection. For other areas accessible to the public it is suggested that you research the Bureau of Land Management web sites.

 

Where to go Rock Hounding in Arizona:

            The following list was obtained from the Bureau of Land Management and indicates areas in which rock hounding is allowed:

 

 

 

 

Black Hills Rock Hounding Area:

Photo: Necole Michael

 

  

            Located 18 miles north of Safford, Arizona the Black Hills Rock Hounding Area is a 2 ½ hour drive from Sierra Vista. This quick and inexpensive day trip will delight children and rockhounders of any age. Managed by the Bureau of Land Management (BLM) there are strict guidelines and several cautionary statements for your treasure hunting experience.
 

There are no restrooms or water available at the site. It is advised that if you plan on venturing out to this area to bring plenty of water. Small stones and fragments can be found atop the ground as the land is frequently plowed for easier access.  However, it is advised that you bring a shovel as many of the more precious and larger samples are located at least two feet under ground. Once you have completed your dig please remember to fill your hole as it can and will present danger to the humans and wild life.  Strict guidelines prohibit the selling of materials obtained during your adventure; you are allowed to take twenty-five pounds of fire agates for your collection and personal enjoyment. In addition to water and a shovel it is also advised that you bring a bucket, chair and plenty of sun block.
 

Photo Credit Necole Michael

 

 Also worth noting this area is free range, Betsy the cow and her friends are often found looming, please watch for cow manure, snakes and other pesky desert creatures. Now that we have discussed the area in which we are going to explore lets discuss what fire agates are.

Photo Credit: Flickr.com

 

 

 

 

What are Fire Agates?

 

 

Photo Credit Necole Michael

 

 

            Fire agates can be characterized by the chemical compound SiO2, the minerals Silica and Iron oxide.  The colors of a fire agate range from clear to brilliant red, orange, blue and green. Beyond color a fire agate can also be described as translucent or opaque. The luster, appearance or quality of light seen in a fire agate is classified as waxy and the streak or color the mineral produces when in powder form is described as white.  Another physical property of fire agates includes cleavage or the tendency of a mineral to break along planes of weakness; for a fire agate this is zero or none. Since there is no cleavage the fire agate is said to fracture in a conchoidal fashion which can be described as smooth and curved similar to broken glass, the edges of a fire agate are sharp. Finally the crystal form, or the external expression of the minerals internal arrangement of atoms, in a fire agate is described as cryptocrystalline. This means that the crystals are small and difficult to identify even with a microscope.

 

 

Photo Credit Necole Michael

How Are Fire Agates Formed?

           

            Volcano eruptions often bestow thoughts of death and destruction; however brilliant gems are often the creation from this naturally occurring disaster. Fire agates are an example of the beauty created by volcanoes. Considered semi precious gem stones fire agates rate a 7 on the Mohs scale of hardness.  Color and pattern formations are unique to each agate, while some may share similar characteristics it is unusual to find agates that have formed identically.
 

The formation of a fire agate begins when hot water, saturated with colloidal silica and iron oxide, invades cavities in country rock and then cools. As the solution begins cooling and evaporating layers of silica begin to grow and iron oxide is deposited. The layers of silica and iron oxide allow for the variant of color in the fire agate. Also affecting the color and layers of the agate are the temperature in which the minerals begin cooling, pressure and the content of the minerals.   

 

Photo Credit: Necole Michael

Conclusion
 

            Rock hounding is a unique experience designed to improve your rock collection and your ability to identify precious minerals.  Arizona offers several areas in which to explore, rules and regulations must be followed for your safety and the safety of the natural species of the area.  Fire agates are an example of the unique gems that you can collect while exploring the Black Hills Rock Hounding area.  Unique and readily available this rock hounding experience will provide the avid rock collector and rock loving child with a wide variety of beautiful fire agates.

             

 

Works Cited

"Agat   "Agate Basics." Agate Basics. 28 Nov. 2007  www.agatelady.com/agate-basics.html
Arizona. Bureau of Land Management. Rock Hounding. http://www.blm.gov/az/outrec/rockhounding/rockhnd.htm
"Fire Agate." Wikpedia. 6 Nov. 2007. 28 Nov. 2007  http://en.wikipedia.org/wiki/Fire_Agate
"Rock Hound." Encarta. 27 Nov. 2007  http://encarta.msn.com/dictionary_1861705781/rock_hound.html
Tarbuck, Edward J., and Fredrick K. Lutgens. Earth Science. 10th ed. Upper Saddle River: Prentice Hall, 2003.