PEACOCK ORE; BORNITE OR CHALCOPYRITE?

Labeled Peacock Ore: Missouri. This specimen is chalcopyrite that has been subjected to an acid bath.  Width ~2.5 cm.

Labeled Peacock Ore: Mexico.  Width: ~2.0 cm.  Chalcopyrite and quartz.

I have always found it interesting that in virtually every rock/mineral show, in most rock shops, and in many curio/souvenir shops, especially in the western U.S, visitors will easily locate specimens of “Peacock Ore” for sale.  In most, but not all, instances vendors will simply market the specimens, at a cheap price, to buyers.  Upon request most sellers will explain that peacock ore is a copper mineral while others might state the ore is a variety of bornite or perhaps chalcopyrite.  Only the most honest proprietors will explain to prospective buyers the history behind peacock ore.  It is very inexpensive and the iridescence is quite attractive so just buy it and take it home for the kids.

Chalcopyrite, Sweetwater Mine, Reynolds County, Missouri.  Width ~6.5 cm.

Chalcopyrite [CuFeS₂] is a copper iron sulfide that is often confused with the iron sulfide, pyrite [FeS₂].  Both are sort of a brassy yellow color and tarnish upon exposure to oxygen.  Chalcopyrite is much softer (3.5-4.0 Mohs) than pyrite (6.0-6.5).  Pyrite (Isometric Crystal System) often occurs as cubes but sometimes as octahedrons and pyritohedrons.  Chalcopyrite (Tetragonal Crystal System) crystals are often shaped like two wedges back-to-back (dispenoid).  Both pyrite and chalcopyrite can have striated crystal faces and also occur as botryoidal masses.  They also are found together but there is something about the color, tarnish and luster than distinguishes the two.

Chalcopyrite is a very common mineral and the major ore of copper occurring as massive mineral deposits to veins to disseminated crystals in the porphyry copper deposits so important in the U.S. 

Massive Bornite and chalcopyrite, Flambeau Mine, Rusk County, Wisconsin.  Width ~ 4.4 cm.

Labeled Bornite (massive) and Galena: Montana.  Width: ~4.2 cm.

The sulfide bornite [Cu₅FeS₄] is also an important copper ore (close to 65% by mass), especially in the copper porphyry deposits.  It is Orthorhombic but commonly is massive and/or granular in habit.  It does not display the brassy color of pyrite or chalcopyrite until tarnished but is a mottled brown/black/purple to copper-red but often is mixed with chalcopyrite. It easily tarnishes upon exposure to air and results in purple/blue iridescence on some areas.  In fact, it is often called “peacock ore!”

So, what are the specimens sold as iridescence peacock ore seen in the markets?  Well, mostly it is chalcopyrite that has been in an acid bath! Sometimes chunks of very iridescent bornite may find their place in sales but essentially peacock ore is altered chalcopyrite: 

CuFeS₂ + 2HCl + 5/4O₂-->CuC_l2 + FeOOH + 1/2H₂O +2S. 

So, can an “amateur” turn chalcopyrite into peacock ore?  I found it interesting that an entire forum on “turning copper pyrite into peacock ore” may be found on www.mindat.com. Statements included:  the trick consists of not rinsing the specimens after treatment but to let them dry; the best results I have had is using plain white vinegar, acetic acid, with a little scrap copper, wire or copper pipe, thrown in. I usually let it set outside covered in the sun for a week or until the color has changed. Pull them out and let dry without rinsing. You can rinse after drying if needed; household bleach (sodium hypochlorite) will also do it (in place of acid).

One of my future projects is to locate some chalcopyrite, dump it in some acid, and see if I can produce some non-realistic looking peacock ore.  Well, at least “fake” peacock ore.  Or is it “real” peacock ore?  If possible to produce I will stick it on my shelf besides the non-realistic looking (dyed) agate.  Who will know?

Some people think that the truth can be hidden with a little cover-up and decoration.  But as time goes by, what is true is revealed and what is fake fades away.
           Ismail Haniyeh