Gabbro refers to a large group of dark, coarse-grained, intrusive mafic igneous rocks chemically equivalent to basalt. Basalt and gabbro have the same chemical composition but basalt is volcanic and gabbro is plutonic — formed when molten magma is trapped beneath the Earth’s surface and cools into a crystalline mass. Gabbro is an essential part of the oceanic crust and is found all over the world. It is commonly found in the core of the Sierra Nevada mountain range as a large batholith or placement of igneous rock.
Gabbro is dense, greenish or dark-colored. It is coarse grained, with large crystals.
Ocellar (spotted) varieties of gabbro can be used as ornamental facing stones and as paving stones. Known by the trade name of ‘black granite’ gabbro is popular for use as graveyard headstones. It is also used in kitchens for countertops under the misleading name of ‘black granite’. A famous example of gabbro can be seen in the Vietnam Memorial Wall.
PHOTOS:
- Gabbro volcanic rock. www.flexiblelearning.auckland.ac.nz
- Galant Gabbro tiles & slabs www.stonecontact.com
- Vietnam Memorial Wall: polished gabbro. Elsa B Walton