Day #5 Deskcrop: Muscovite Book

Today’s deskcrop comes from the Dan Patch Pegmatite Mine Dump, located just west of Keystone and just north of Mount Rushmore in the Black Hills of South Dakota.

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Muscovite and Quartz

Most of the muscovite at the dump is fairly weathered and flakes apart easily. However, some intact books can be found.

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Note the Pseudohexagonal Crystal Form

This one displays a beautiful pseudohexagonal crystal form, but don’t be deceived – muscovite is monclinic!

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The Hexagons Don’t Stack Vertically, However,
Making Muscovite a Member of the Monoclinic Crystal System

The Dan Patch Mine is owned by the Pacer Corporation of Custer, SD. Obtain permission before visiting or collecting.

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