Gabbro
Gabbro refers to a large group of dark, coarse-grained, intrusive igneous rocks chemically equivalent to basalt. The vast majority of the Earth's surface is underlain by gabbro within oceanic crust, produced by basalt magmatism at mid-ocean ridges. Gabbro is dense, greenish or dark-colored and contains pyroxene, plagioclase, amphibole, and olivine (olivine gabbro when olivine is present in a large amount). The pyroxene is mostly clinopyroxene whereas small amounts of orthopyroxene may be present. If the amount of orthopyroxene is substantially greater than the amount of clinopyroxene, the rock is then a norite. Quartz gabbros are also known to occur and are probably derived from magma that was over-saturated with silica. Essexites represent gabbros whose parent magma was under-saturated with silica, resulting in the formation of the feldspathoid mineral nepheline. Gabbros contain minor amounts, typically a few percent, of iron-titanium oxides such as magnetite, ilmenite, and ulvospinel. Gabbro is generally coarse grained, with crystals in the size range of 1 mm or greater. Finer grained equivalents of gabbro are called diabase, although the vernacular term microgabbro is often used when extra descriptiveness is desired. Gabbro may be extremely coarse grained to pegmatitic, and some pyroxene-plagioclase cumulates are essentially coarse grained gabbro, although these may exhibit acicular crystal habits. Gabbro is usually equigranular in texture, although it may be porphyritic at times, especially when plagioclase oikocrysts have grown earlier than the groundmass minerals.


Photographed by Michael P. Klimetz

SCOTLAND
Photographed by Michael P. Klimetz

SCOTLAND
Photographed by Michael P. Klimetz

[With Hornblende]

Stillwater
MONTANA
Photographed by Michael P. Klimetz

[With Hornblende]

Salem
MASSACHUSETTS
Photographed by Michael P. Klimetz


Stillwater
MONTANA
Photographed by Michael P. Klimetz


Stillwater
MONTANA
Photographed by Michael P. Klimetz


Florence County
WISCONSIN
Photographed by Michael P. Klimetz


Stillwater
MONTANA
Photographed by Michael P. Klimetz


Comanche County
OKLAHOMA
Photographed by Michael P. Klimetz


Diabase


Palisades Interstate Park
Alpine


Bergen County
NEW JERSEY
Photographed by Michael P. Klimetz

Troctolite Gabbro


Balmedie


SCOTLAND
Photographed by Michael P. Klimetz

Troctolite Gabbro


Balmedie


SCOTLAND
Photographed by Michael P. Klimetz

Troctolite Gabbro


Balmedie


SCOTLAND
Photographed by Michael P. Klimetz

Olivine Dolerite


Waterswallows Quarry
Buxton


Derbyshire
UNITED KINGDOM
Photographed by Michael P. Klimetz

Olivine Dolerite


Waterswallows Quarry
Buxton


Derbyshire
UNITED KINGDOM
Photographed by Michael P. Klimetz

Garnet-Gabbro


Finero
Ivrea Zone


Val Cannobio
ITALY
Photographed by Michael P. Klimetz

Hypersthene/Olivine-Gabbro
[Partially Serpenitized]

Baltimore Mafic Complex
Cambrian
Cedar Hill Quarry

Lancaster County
PENNSYLVANIA
Photographed by Michael P. Klimetz

Hypersthene/Olivine-Gabbro
[Partially Serpenitized]

Baltimore Mafic Complex
Cambrian
Cedar Hill Quarry

Lancaster County
PENNSYLVANIA
Photographed by Michael P. Klimetz

Hypersthene/Olivine-Gabbro
[Partially Serpenitized]

Baltimore Mafic Complex
Cambrian
Cedar Hill Quarry

Lancaster County
PENNSYLVANIA
Photographed by Michael P. Klimetz

Hypersthene/Olivine-Gabbro
[Partially Serpenitized]

Baltimore Mafic Complex
Cambrian
Cedar Hill Quarry

Lancaster County
PENNSYLVANIA
Photographed by Michael P. Klimetz

Hypersthene/Olivine-Gabbro
[Partially Serpenitized]

Baltimore Mafic Complex
Cambrian
Cedar Hill Quarry

Lancaster County
PENNSYLVANIA
Photographed by Michael P. Klimetz

Hypersthene/Olivine-Gabbro
[Partially Serpenitized]

Baltimore Mafic Complex
Cambrian
Cedar Hill Quarry

Lancaster County
PENNSYLVANIA
Photographed by Michael P. Klimetz

Hypersthene/Olivine-Gabbro
[Partially Serpenitized]

Baltimore Mafic Complex
Cambrian
Cedar Hill Quarry

Lancaster County
PENNSYLVANIA
Photographed by Michael P. Klimetz

Hypersthene/Olivine-Gabbro
[Partially Serpenitized]

Baltimore Mafic Complex
Cambrian
Cedar Hill Quarry

Lancaster County
PENNSYLVANIA
Photographed by Michael P. Klimetz

Olivine-Gabbronorite
[Partially Serpenitized]

Coast Range Ophiolite

Point Sal

Santa Barbara County
CALIFORNIA
Photographed by Michael P. Klimetz

Olivine-Gabbronorite
[Partially Serpenitized]

Coast Range Ophiolite

Point Sal

Santa Barbara County
CALIFORNIA
Photographed by Michael P. Klimetz

Hornblende Gabbro

Mesozoic
Pine Flat Complex

Pine Flat Lake

Fresno County
CALIFORNIA
Photographed by Michael P. Klimetz

Hornblende Gabbro

Mesozoic
Pine Flat Complex

Pine Flat Lake

Fresno County
CALIFORNIA
Photographed by Michael P. Klimetz

Hornblende Gabbro

Mesozoic
Pine Flat Complex

Pine Flat Lake

Fresno County
CALIFORNIA
Photographed by Michael P. Klimetz

Hornblende Gabbro

Mesozoic
Pine Flat Complex

Pine Flat Lake

Fresno County
CALIFORNIA
Photographed by Michael P. Klimetz

Hornblende Gabbro

Mesozoic
Pine Flat Complex

Pine Flat Lake

Fresno County
CALIFORNIA