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Important Rocks & Minerals

MINERALS: Naturally occurring compounds with characteristics properties and chemical composition.

Primary minerals form from magma deep within the earth.
Secondary minerals form during weathering at the surface of the earth.

Quartz QUARTZ
(primary mineral)

  • translucent, often milky
  • irregular surface, not planar
  • very hard

Composition: SiO2

Found in: many rocks, esp. light-color (felsic), sandstones.

Muscovite
Muscovite
Biotite
Biotite
MICAS
(primary minerals)

  • platy, sheet-like
  • black (biotite) or clear (muscovite)
  • soft, can be peeled

Composition: (Al, Si + O) with K

Found in: many igneous and metamorphic rocks.

Feldspar FELDSPARS
(primary minerals)

  • angular, sharp crystal faces/edges
  • tan to brown, pink, whitish

Composition: (Al, Si + O) with K

Found in: many igneous and metamorphic rocks.

Ferromag-basalt FERROMAGNESIAN MINERALS
(primary minerals)

  • angular, sharp crystal faces
  • black or very dark green

Composition: (Al, Si + O) with Mg, Fe

Found in: dark (mafic) igneous rocks.

Hematite
Hematite
Goethite
Goethite
IRON OXIDES >>HEMATITE, GOETHITE
(secondary minerals)

  • dull, seldom crystalline
  • dull red (hematite) to yellow (goethite)
  • usually soft, dense masses

Composition: Fe(O,OH)Found in: sedimentary rocks; saprolite.

Kaolinite
Kaolinite
Vermiculite
Vermiculite
CLAY MINERALS >>KAOLINITE, VERMICULITE
(secondary minerals)

  • dull; seldom crystalline
  • whitish to grey
  • soft

Composition: (Al, Si, O)

Found in: sedimentary rocks; saprolite.


ROCKS: Assemblage of minerals; a fixed proportion of various minerals present give characteristic appearance & properties.Igneous rocks form from the cooling of magma.
Metamorphic rocks form from alteration (pressure, heat).
Sedimentary rocks form from cemented sediments in the ocean floor.

Granite GRANITE
(igneous rock)

  • Light colored (mafic); fine to large crystals.
  • Uniform texture (no banding).

Composition: Largely quartz, feldspar; some mica.

Found in: Intrusive bodies in Piedmont (Stone Mt).

Basalt BASALT
(igneous rock)

  • Dark colored (mafic); fine to very fine crystals.
  • Uniform texture (no banding).

Composition: High in ferromagnesian minerals (hornblende, augite).

Isolated occurrence in Piedmont (seafloor remnants deposited during orogeny).

Schist SCHIST
(metamorphic rock)

  • Intermediate to dark colored; fine to coarse crystals.
  • Finely banded (foliated), light and dark.

Composition: Commonly mica, with quartz, feldspar.

Formed from metamorphosed sediments; common in Piedmont, Blue Ridge.

Gneiss GNEISS
(metamorphic rock)

  • Intermediate to light color; medium – coarse crystals.
  • Coarsely banded, fine dark bands/coarse light bands.

Composition: Quartz, feldspar, mica.

Formed from metamorphosed granites or sandy marine sediments; common in Piedmont, Blue Ridge.

Limestone LIMESTONE
(sedimentary rock)

  • Whitish to light grey; few crystals; may contain fossils.
  • May be coarsely or finely banded, or massive.

Composition: Calcite, with mixture of clay minerals.

Formed in off-shore marine environments; common in Valley & Ridge, parts of Coastal Plain.

Sandstone SANDSTONE
(sedimentary rock)

  • Various colors (grey, brown, tan, reddish).
  • Feels sandy when rubbed.
  • May or may not be banded.

Composition: Quartz with some oxides.

Formed in near-shore marine deposits; common in Valley & Ridge, parts of Coastal Plain.

Shale SHALE, SILTSTONE
(sedimentary rock)

  • Usually grey/brownish grey (also tan to red).
  • Finely layered (foliated); often soft, easily broken (siltstone).

Composition: Clay minerals with accessory minerals (oxides).

Formed in near-shore marshes, or in deep-water marine environments; common in Valley & Ridge.