Gabbro is a dark, coarse-grained intrusive
igneous rock chemically equivalent to
basalt. It is a
plutonic rock, formed when molten magma is trapped beneath the Earth's surface and cools slowly into a hard, coarsely crystalline mass. It is dense, greenish or dark-colored and contains varied percentages of plagioclase
feldspar,
pyroxene,
amphibole, and
olivine (called olivine gabbro when olivine is present in large quantities).
Quartz gabbros are also known to occur and are probably derived from
magma that was oversaturated with
silica. On the other hand,
essexites[?] represent gabbros whose parent magma had an insufficiency of silica resulting in the formation of
nephelite[?].
Gabbro is too fragile to use in construction, but often contains valuable amounts of chromium, nickel, cobalt, gold, silver, platinum, and copper sulfides[?].
See also: List of minerals
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