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  Latest Training
IGNEOUS ROCKS
Publisher date : June 2008
Chapter title : IGNEOUS ROCK CLASSIFICATION
Data title : DUNITE

  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 (see "Another specimen".)
      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

  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).


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