schist - teaching hand specimen of silvery quartz-mica schist with wavy parting

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Teaching hand specimen of shimmering silvery quartz-mica schist with wavy parting
The silver quartz-mica schists of the Precambrian Mayo Formation are exposed along Highway 16 west of Custer, South Dakota. Biotite is the predominant mica. Tilted back and forth, the quartz imparts a shimmering silvery flash. Derived from sedimentary rocks, it was metamorphosed from graywacke and silty shale. Graywackes are essentially dirty sandstones.
Schist is part of the metamorphic series that begins with a shale parent, proceeding with increasing regional metamorphism through slate, phyllite, schist and gneiss. If the gneiss is partly melted, migmatite forms. Complete melting produces an igneous rock in the family of granite.
Students should be able to identify a schist when it is tilted back and forth from the satiny sheen given by mica flakes that squeezed into alignment. A schist usually breaks along the plane of the mica. Metamorphism has given this schist a wavy parting surface. The silvery shimmer from the quartz grains and the wavy parting are spectacular.
Collected along North Pole Road in the Berne, South Dakota quadrangle. USGS Professional Paper 297F covers the area.
These specimens will fit into a 3.5” x 5.25" specimen tray. We include data with every specimen: collecting locality for mineral specimens and for rocks also the formation and age, if determined.
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