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.

Muscovite and Quartz

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

Note the Pseudohexagonal Crystal Form

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

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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