Columbite-Tantalite
Etta Mine, Keystone, Keystone Mining District, Pennington County, South Dakota, USA
5.3 x 5.2 x 2.0 cm. Mineral specimens of any species are very rare from this pegmatite, renowned for huge beryl, spodumene and feldspar crystals. This sharp, euhedral, tabular, blocky, layered, black columbite-tantalite crystal has highly lustrous striated faces and matte-finish faces. Probably older material; and rare in this sharp, ...
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