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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