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Roger Weller, geology instructor

wellerr@cochise.edu


Garnets
by Heather O'Conner
Physical Geology
Spring 2007     

Garnets

            Not only is garnet a nice piece of jewelry it is a part of history. It has been said to have healing powers and is known for its original folklore and legends. There are mythological remnants of the garnet.                                                                 
                                                                           
                                                                                              photo by R.Weller/Cochise College

          Mythology and legends of garnets date back to even, the prehistoric times. Before Europe was Europe there existed a village of “Lake Dwellers”. They wore garnets around their necks probably to heal or protect from evil spirits. Garnets were even the first to ever be mentioned in ancient writings. Garnets also have a deep history with ancient warriors and journeyers, also probably for protection and a form of faith. Garnet’s powers include healing, strength, and protection. People often wore garnets to relieve inflammation of the skin, and it is said to regulate the heart, blood flow, and aid in curing depression. Also in early times garnets were given between friends to show how much they care for each other and to insure they will be together again.


photo by R.Weller/Cochise College

           Garnet the January birthstone is naturally occurring mineral gemstone. The name garnet comes from the Latin word “granatus” meaning seed or grain. This is because when it is mined, it resembles seeds in the original matrix (rock) that surrounds it.  Garnet originates in a family of relative minerals. They have similar physical and crystalline properties. Majority becomes stones. All garnets have the same chemical formula but different components. It is popularly known for it being, a dark red stone which is inexpensive. Known as “only garnet”, it was thought to inferior.
 

       
photo by R.Weller/Cochise College                                                                                    
 

Garnet occurs in many colors other the original dark red color. It extends to other rare and attractive forms. These all are separated into two family groups. One family group in made up of aluminum silicates (metal). The second family group is made up of calcium silicates (metal). The colors include oranges, browns, greens, and yellows.
 

               photo by R.Weller/Cochise College

These variations in color reflect the compositions of the garnet species. They are:

·        Almandite; an iron aluminum silicate-Fe₃Al₂Si₃O₁₂

·        Pyrope: a magnesium aluminum silicate-Mg₃Al₂Si₃O₁₂

·        Spessartite; a magnesium aluminum silicate-Mn₃Al₂Si₃O₁₂

·         Andradite, a calcium iron silicate-Ca₃Fe₂Si₃O₁₂

·        Grossularite; a calcium aluminum silicate-Ca₃Al₂Si₃O₁₂

·        Uvarovite; a calcium chromium silicate-Ca₃Cr₂Si₃O₁₂
 

            These numbers and letters represent the formula that makes up each species of garnet. The chemical composition formula for it is quite general.

The chemical composition formula for a garnet is like this: D₃T₃ (SiO₄)₃.  The letter “D” stands for a divalent metal-like calcium, magnesium, ferrous iron, or manganese. The letter “T” stands for a trivalent metal–like aluminum, ferric iron, or chromium.   It is rarely that few garnets have precise pure chemical compositions.  Almost all garnets are of mixed types. This is where one type is partially replaced by another type.

photo by R.Weller/Cochise College
 
            Garnet does have some rare species that reflect the change in chemical compositions that reflect the wide range of substitutions that its crystal structure can accommodate. They include:

·        Hydrogrossular-Ca₃AI₂(SiO₄)₃-x(OH)₄

·        Henritermierite-Ca₃(Mn,AI)(SiO₄)₂(OH)₄

·        Goldmanite-Ca₃V₂Si₃O₁₂

·        Kimzeyite-Ca₃(Cr,Ti)₂(AI,Si)₃O₁₂

·        Knorringite-Mg₃Cr₂Si₃O₁₂

·        Majorite-Mg₃(Fe,AI,Si)₂Si₃O₁₂

·        Schorlmite-Ca₃(Fe,Ti)₂((Si,Ti)O₄)₂

·        Yamatoite-Mn₃V₂Si₃O₁₂ 


photo by R.Weller/Cochise College
 

            There is a really rare garnet named demantoid, named because it resembles a diamond-like crystal luster and color. It is found in Russia and is the softest garnet found. Demantoid is a bright grassy green gem that is running out of supply, because it is so well liked.  Another rare gem is the tsavolite garnet. It is a bright green gem, induced by the presence of chromium. Next is topazolite garnet, named because of the topaz-yellow color or even olive green color. The last is the reddish “African” garnet. They are found in close association with diamonds, showing distinct magnetism.

You can find garnets all across America too. At first, garnets were used industrially as coated sandpaper, by Henry Hudson Barton (who founded Barton Mines Corporation).  Arizona is one of those states that mine garnets. It is also one of the five states that have commercial production of gem garnets. One can find these in the Apache county and Navajo Indian Res. The gems there are red in color and can get up to five carats in size. In New York, 3,000 miles away,  you can find garnets as well. Deposits of industrial garnets are found in two different locations. They are mined in Gore Mountain area and near the town of Willsboro.

In Gore Mountain. the garnets found there are imperfectly developed. They are crystals surrounded by a rim of coarsely crystalline hornblende. As for the deposits in Willsboro they are good enough to produce fine facet-grade garnets. These garnets are solid solutions that result in a pleasant deep brownish red material, which often has an orange cast. It can be cut into beautiful small stones, but larger stones are too dark to be attractive.

As for the trade world, gem dealers don’t usually call their finds by their scientific name.  Basically they name it after where they found the stone. An example would be the brown garnet known as the “Indian” garnet. Some garnets are named for their colors.  Hessonite is a fine orange color, cinnamon brown color, or pinkish variety of the grossularite garnets. Then there is tsavorite, which is the trade name for fine dark green grossularite.  Also there is melanite, a black color gem.  Malaya is the trade name for the red shades through the orange shades, as well as peach to pink shades. Finally there is rhodolite, which is the purplish red solid solution garnet.


photo by R.Weller/Cochise College

            All species of garnet have been used as gemstones. Garnet displays the greatest Varity of color of any mineral, occurring in every color except blue. Garnet has history and spice. It has mystery and beauty. It is January’s birthstone and great as a pair of earrings.


photo by R.Weller/Cochise College