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10/09/08
subsaturate silicates

The easiest way to sum up the chemical composition of the subsaturate group is to say these have extra oxygen ions.  Examples are kyanite, staurolite, sillimanite, andalusite, and topaz.   I just recently acquired a sample of the kyanite and found it attractive with its underlying blue shimmer.  My specimen comes from North Carolina.  Staurolite is found in a range from New England to Georgia, also in Sweden, and often forms cruciform crystals that can be made into cross jewelry.  Sillimanite has the same composition as kyanite but a different structure and is a bit harder.  Andalusite also has the same chemical composition as kyanite and sillimanite.  It forms at lower temps and is sometimes faceted and used as a gem.  Everyone knows topaz.  It has a similar structure to other subsaturates but is otherwise unrelated.  Topaz can be found in a variety of colors.  The amber colored is the birthstone for November.


Posted by oh5/ojhoff at 2:46 PM CDT
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