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04/21/09
more about feldspar

The plagioclase feldspars are a solid solution series.  The end stones are albite and anorthite.  Intermediate specimens include labradorite, a well known gem when it's chatoyant, and bytownite, found in Minnesota.

The feldspathoid group are framework silicates containing less sillica than the feldspars.  These were formed in silica-poor areas and therefore are not found in areas where there is a lot of quartz.  Sodalite belongs to this group.  

Two other related groups are scapolite, which in its yellow form has been used as a gem, and the zeolite group which includes 22 well defined species.  The zeolite group includes stilbite, chabazite and heulandite, all of which form into beautiful crystals.


Posted by oh5/ojhoff at 10:01 PM CDT
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