Detail
Another specimen
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| GABBRO
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Typical Minerals Ca PLAGIOCLASE & PYROXENE about 50/50Amphibole often present Olivine - absent to trace | Description
A mafic igneous rock from the top of Bowen's Reaction Series. Typically dark colored with a mixture of dark gray calcium plagioclase and dark colored (dark green to black; dull; not showing good cleavage) pyroxene. Although the plagioclase may be dark gray it can also be light gray (as in this specimen) or even white. What is critical here is the prominence of pyroxene from the top of Bowen's Reaction series, although it may be mixed with amphibole. Olivine is sometime present but is not essential. |
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Tectonic Association
Gabbro 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
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| Last Update: 9/29/00 | e-mail: (Fichtels@jmu.edu) |