Ig. Home | Simp.Class. | Advanc.Class. | Alpha.List | Bowen's Reac.Srs. | ID Keys | Extrus/Intrus | Tect. | Self Tests
DUNITE

   Detail
     

Return to previous specimen

  Return to Classification; pdf version
Typical Minerals
OLIVINE >90%

Pyroxene may be present, as well as black chromite crystals. NO feldspars!
     When pyroxene is between 10-60% the rock is called Peridotite.
Description
     An ultramafic igneous rock from the top left side of Bowen's Reaction Series. Typically pale green (olive green) in granular masses. Massive varieties sometimes exist.
      What is notable about the rock is the absence of feldspars of any kind. Feldspars are so common (some 56% of the earth's crust) that when they are absent it says something special is going on.
      When pyroxene exceeds 10% and heads up toward 60% the rock is named Peridotite.
   Return to Classification; pdf version
   Return to Previous Rock
Tectonic Association
      Dunite (and peridotite) is typically found on continents in dikes, sills, and laccoliths associated with mafic igneous bodies. The concentration of olivine may occur through gravity settling, as well as other mechanisms. Dunite/peridotite is also a common constituent of the oceanic lithosphere (ophiolite suite) forming below the crust in the mantle (below the Moho boundary).
   Tectonic Cross Section - pdf version

LSF Home | Geology Web Sites | Courses | JMU Geology
Last Update: 9/29/00

e-mail: (Fichtels@jmu.edu)