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