• Specimen Number

  39

• Description

  White and rusted block of vein pegmatite. Survey staff identify it as being composed of "albite, perthitic microcline, oligoclase, muscovite and quartz with accessory minerals of tourmaline, biotite, apatite and garnet.  Occurs as sills, dikes, and large irregular bodies mostly of feldspar and quartz."

• Classification

  Hydrothermal. Pegmatite.

• Location & Occurrence

  Survey staff suggest that pegmatite is from the Harney Peak Granite (formation). Likely from an abandoned mine in the southern Black Hills either near Keystone or Custer.

• Geologic Age

  Proterozoic. 1.7 Ga

• Geoheritage

  This formation underlies the state's highest peak, Black Elk Peak, formerly Harney Peak. Quoting the survey staff:  "If the specimen was collected in the 1930’s, the pegmatites then were being heavily mined for Lithium, Beryllium, Mica and Tin.  In the 1950-60s, South Dakota was the largest producer of Lithium and Beryllium."

• Links

  Link to State Geological Map from USGS.  Link to South Dakota Geological Survey Program .

• Other

  Specimen bears strong resemblance to specimen #22 from Mississippi with same milky white color, gray blotches, oxide stains, flat surfaces, straight jagged edges, and consistency of acute fracture angles,  same oxide stain.  This resemblance suggests that two samples of this stone were used for two states.

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