Monday, January 21, 2013

Garnets





Garnet is a family of minerals and not just one specific mineral or color.  The garnet family is very complex with a wide diversity in color and chemical composition.
There are 15 different types of garnet but only six are commonly found.  To make matters more confusing, the garnets can, and usually do, mix together creating different colors adding to the confusion. 
Garnets are defined by their chemical composition.
Species        Color                Elements
Pyrope        vivid red to purple red    Mg, Al
Almandine        dark red-purple-brown    Fe2+, Al
Spessartine        redish brown        Mn2+, Al
Grossular        green to brown        Ca, Al
Andradite        Dark red to redish brown    Ca, Fe
Uvarovite        Vivid lime green        Ca, Cr   
Utah has a couple of different types of garnets showing a variety of color. 
The four corners area contains vivid pyrope garnet pebbles the size of a bb to a pea that are found in the ant hills.  These little pebbles are dug up by the ants and deposited on top of the mounds.  Collectors screen the ant hills in search of these gem treasures.  Pyrope garnets cut very clean vivid red stones, usually smaller than a ½ carat.

The Wah Wah Mountains contain a skarn that produce an unusual pale lime green garnet called grossular.  Most of the garnets from here are too included to make good faceted gemstones so they is cut into cabochons.  Searching the edges of the crystals may produce a piece big enough to facet a smaller size stone.
In the Mineral Mountains a different type of garnet is found.  It is actually 2 types of garnets mixed into one stone; spessartine and andradite form together in a solid solution forming an intermediate kind of garnet of an orange-ish red color.  These garnets are rarely big enough to cut stones over ½ carat but the color is very desirable.
There is a garnet schist in Dagget County that has produced a lot of reddish-brown garnets but few are of gem grade.
There are many other garnet locations in Utah but none that produce anything in the way of a gemstone.  Places like the Thomas Range, Little Cottonwood Canyon, and the Gold Hill mine to name a few.  Some material from these locations can be cut into cabs of much lesser quality. 

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