Etta Mine, Keystone, Keystone District, Pennington Co., South Dakota, USA

A lithium-niobium/tantalum-tin muscovite mine in pegmatite. Started in 1883. Owned by the Harney Peak Tin Co. This mine is famous for its huge crystals.

Originally exploited for muscovite in 1883, but acquired by the Harney Peak Tin Mining Company. Tin was never encountered in economic concentrations and the company collapsed by 1893 in "The Black Hills Tin Scandal".

Lithium (spodumene) mining commenced in 1898 and ceased in 1959. Over the years, the mine produced muscovite, niobium, tantalum, beryl and feldspar.

References:
Dana, E.S. (1892) System of Mineralogy, 6th. Edition, New York: 1088.

Rocks & Minerals: 10: 121-122, 146-147.

Rocks & Minerals: 57: 160.

Rocks & Minerals: 60: 110, 112.

Rocks & Minerals: 75(3): 156-169.

http://query.nytimes.com/gst/abstract.html?res=9506E0DB1338E533A25755C0A9649D94669FD7CF

http://giantcrystals.strahlen.org/america/etta.htm

"A History of Black Hills Pegmatites", Matrix Magazine, Volume 10, Number 3, Tom Loomis