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     The final leg of the journey is to the far southwest corner of Minnesota in search of Sioux Quartzite.  The first stop is at the Pipestone National Monument at the northwest end of Pipestone, MN.  At the entrance to the park are six huge boulders called the Three Maidens. 
     The sign in front of the boulders says that many American Indians believe that the large boulders shelter the spirits of maidens who require offerings before permitting them to quarry pipestone.  The rocks are actually granite (close up photo below) carried here by glaciers (glacial erratics).  It is estimated that the rocks came as one huge boulder about 50 feet in diameter that split into six pieces by continued freezing and thawing actions.

     A few yards to the southeast of the Three Maidens is an old rock quarry where Sioux Quartzite is visible.  This is actually orthoquartzite, a sedimentary rock not a true quartzite that is metamorphic sandstone.  This rock is sand cemented together by silica.  Silica is essentially evaporated sand solution.   Sand left over by erosion, probably from granite, was carried here by streams and deposited as a lake or ocean shore.  The water dissolved some of the sand and when it evaporated the silica precipitated out to cement together the sand grains.  Looking at thin section micrographs of the rock it is possible to see the rounded grains of the sand without any evidence of metamorphic activity.  The quartzite is quarried in a number of places including New Ulm and Jasper Minnesota.  The geology of the quartzite makes it difficult do date.


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