• Specimen Number

  38

• Description

  Rhomboid block of granite gneiss with large, feldspar porphyroblasts.  Identified by state survey as an "augen gneiss," one of several in the state. Their informed guess is the  Henderson gneiss.  Our closeup matches their description of "pink-brown k-spars, milky plagioclase, gray quartz, flakes of biotite, and grains of amphibole."

• Classification

  Metamorphic. Gneiss. Augen.

• Location & Occurrence

  Gneiss underlies several iconic bald mountain tops in northwestern part of state including Table Rock and Ceasar's Head.  Must be massive enough to exfoliate. The origin suggested by the survey staff is  "accretion of Iapetan sea-floor and peri-Gondwanan Island arc terranes to Laurentian margin."

• Geologic Age

  Ordovician.  U/Pb zircon of 460-450 Ma.

• Geoheritage

  The uniformity of the granite leads to exfoliation, which leads to curved balds.  The term "augen gneiss" translates to "eye gneiss" because the porphyroblast crystals resemble the shape of eyes.

• Links

  Link to State Geological Map from USGS.  Link to South Carolina Geological Survey .

• Other

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