Cochise College                Student Papers in Geology    
Geology Home Page                          physical geology  historical geology  planetary  gems

Roger Weller, geology instructor                             

wellerr@cochise.edu
 


Malachite/Azurite
Jesse Smith
Physical Geology
Fall 2005

                        The Special Relationship between Azurite and Malachite

 

Top left and right photo’s by Jeffery A. Scovil, bottom left “Malachite Lion” photo by Cindy Fowler, bottom right “Wave Carving” photo courtesy of www.wehug.com
 

     Having lived in Bisbee for the past fourteen years I’ve had a lot of exposure to the breathtaking minerals Azurite and Malachite.  (There are some gorgeous specimens on display at the Bank of America downtown) While I knew they often occurred together and had a special relationship I never knew what it was or the reason why. After doing some research I found out that Azurite and Malachite are almost chemically identical. Compare their chemical formulas and you will see what I mean.

Azurite’s Formula: Cu3 (CO3)2(OH)2

Malachite’s Formula: Cu2(CO3)(OH)2
 

     Notice the “charges of the copper ions are the same for both minerals at positive 2; each hydroxide has a charge of negative one and each carbonate has a charge of negative two.” What causes the color change from Azurite to Malachite when the “charge on the copper remains the same?” Consider a rewrite of their formals.
                                                   Azurite = Cu(OH)2.2(CuCO3)

Malachite = Cu(OH)2.CuCO3
 

     Did you notice the different amounts of CuCO3 in the two formulas above? Azurite has an extra CuCO3, but the transformation can be “explained by an addition of an extra Cu(OH)2 to Azurites formula.” Since the Cu(OH)2 is more oxidized than the CuCO3 the malachite is therefore more oxidized than azurite and “represents a later stage of oxidation and the increased oxidation is what causes the color change.”  Simply put the difference between the two minerals is that azurite holds less water that malachite. But this small difference in water and its reaction with copper content accounts for a wide variety of wonderfully colored specimens that truly amazing.
 

                 

Photos by R. Weller/Cochise College

 

     The word azurite comes from the Persian word “lazhward” meaning blue.  Specimens contain divers blue hues ranging from azure-blue to very dark blue, and in larger crystals almost black. It can also be found in small crystals or crusts.  It rates a 3.5-4 on the Mohs scale of hardness and its luster can be dull, pearly to velvet like, or waxy to subvitreous. 

     The word malachite is derived from the Greek word “moloche” which means mallow, a reference to the minerals leaf-green color. It has divers green hues, some dark and typically banded. Its luster can be dull, earthy, pearly to velvet like, silky, or waxy to subvitreous. It rates the same as azurite on the Mohs scale of hardness with a 3.5-4.


       

Photos by R. Weller/Cochise College

 

     Malachite was allegedly recovered from mines in the Suez-Sinai area as early as 4000 B.C. and was said to have been used as a cure for convulsions and as a powerful local anesthetic.  However its dust can be highly toxic!  Today malachite is used widely as beads for large cabochons which can be used in pedants, brooches, bolo ties, and belt buckles.  Small carvings can also be found, (see opening photo) and its even been used as veneer for table tops.

 

 

                       

Photos by R. Weller/Cochise College

 

     In ancient times azurite was crushed and used as a pigment in medieval manuscripts, glasses and glazes.  Azurite paints “made centuries ago have undergone the transformation much to the imagined horror of artists whose paintings of beautiful blue skies now have a most unusual green hue.” And of course, azurite is very popular in jewelry.

Specimens of azurite and malachite have been obtained from numerous locations world wide and throughout the centuries; from the Democratic Republic of the Congo (formerly know as Zaire), to New Wales, Australia, and it is even found in our own backyard of Bisbee, Arizona.
 

              

Photos by Jesse Smith of Bisbee azurite/malachite specimen

 

     As you can see from the many photos provided on this site the end result of the carbon dioxide and water weathering copper ore or, copper ore weathering calcite, has produced some truly breathtaking specimen. I think these two minerals outshine all others in their unique formation and the end results they produce.

 

 

“Azurite and Malachite are like chocolate and peanut butter, they are always great together”-Stuart
 

         

Photos by R. Weller/Cochise College

 

 

WORKS CITED

http://www.cst.cmich.edu/users/dietr1rv/malachite.htm

http://mineral.galleries.com/minerals/carbonat/azurite.htm

http://www.rockhounds.com/rockshop/azurit2.html

http://www.minerals-n-more.com/Azure_Mala_Info.htnl

http://eprints.qut.edu.au/archive/00001024