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Typical MineralsCa PLAGIOCLASE & PYROXENE about 50/50
Amphibole often present
Olivine - absent to trace
DescriptionA mafic igneous rock from the top of Bowen's Reaction Series. This specimen appears darker than the last one and is closer to what we expect in a color/texture classification, a coarse-grained dark-colored rock. And although there is more dark gray plagioclase here, there is still a lot of light colored plagioclase too. What is crucial, of course, is the prominence of pyroxene as the mafic mineral. The next specimen is darker yet and more what we expect a gabbro to look like.
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Tectonic AssociationGabbro is typically found on continents in dikes, sills, and laccoliths from slow cooling of mafic magma, mostly derived from hot spots. Gabbro is also part of the oceanic lithosphere (ophiolite suite) forming as a thick layer below the top-most pillow lavas across all the oceanic floors.
Tectonic Cross Section - pdf version
|Last Update: 9/29/00||