Muscovite

specimen number:
9862001

location:
Diamond Mica Mine, Pennington Co., South Dakota, USA

description:
A sharp lustrous crystal of muscovite 4.5 cm in size on a quartz matrix. In good condition, this is quite fine for the species.

The Diamond Mica Mine, located near Keystone in the historic mining district of Pennington County, South Dakota, is part of the rich pegmatite belt of the Black Hills. Geologically, the deposit consists of Precambrian complex granitic pegmatites that intruded into regional metamorphic schists, forming zoned structures enriched in coarse-grained rock-forming minerals. Mineralogically, the site is well known for producing exceptional specimens of muscovite mica in large crystalline books, alongside quartz, feldspar, and associated pegmatite accessory minerals. Historically, the mine operated as part of the broader South Dakota mica and strategic mineral booms that intensified during the late nineteenth and mid-twentieth centuries to supply industrial and electrical manufacturing needs.

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