Geologic units in Polk county, North Carolina

Migmatitic Granitic Gneiss (Ordovician/Cambrian) at surface, covers 35 % of this area

Foliated to massive, granitic to quartz dioritic; biotite gneiss and amphibolite common.

Biotite Gneiss and Schist (Cambrian/Late Proterozoic) at surface, covers 33 % of this area

Inequigranular, locally abundant potassic feldspar and garnet; interlayered and gradational with calc-silicate rock, sillimanite-mica schist, mica schist, and amphibolite. Contains small masses of granitic rock.

Mica Schist (Cambrian/Late Proterozoic) at surface, covers 14 % of this area

Garnet, staurolite, kyanite, or sillimanite occur locally; lenses and layers of quartz schist, micaceous quartzite, calc-silicate rock, biotite gneiss, amphibolite, and phyllite.

Inequigranular Biotite Gneiss (Cambrian/Late Proterozoic) at surface, covers 12 % of this area

Weakly foliated to massive, contains plagioclase megacrysts and, rarely, larger megacrysts of quartz and feldspar.

Porphyroblastic Gneiss (Cambrian/Late Proterozoic) at surface, covers 5 % of this area

Massive to foliated, granodioritic, migmatitic.

Garnet-Mica Schist (Cambrian/Late Proterozoic) at surface, covers 0.9 % of this area

Interlayered with amphibolite.

Migmatitic granitoid gneiss (Ordovician) at surface, covers < 0.1 % of this area

Variably foliated, variably migmatitic, and granitic to quartz dioritic in composition

Sillimanite-mica schist and muscovite-biotite schist (Cambrian or Neoproterozoic) at surface, covers < 0.1 % of this area

Thin to thick layered sillimanite-mica schist and sillimanite-bearing muscovite-biotite schist

Megacrystic biotite gneiss (Cambrian or Neoproterozoic) at surface, covers < 0.1 % of this area

Variably layered biotite-quartz-feldspar gneiss having porphyroclasts and/or porphyroblasts of plagioclase and locally of quartz and potassium feldspar

Biotite gneiss and muscovite-biotite gneiss (Cambrian or Neoproterozoic) at surface, covers < 0.1 % of this area

Layered biotite-quartz-feldspar gneiss