Dunite is a plutonic igneous rock, of ultramafic composition, with coarse-grained or phaneritic texture. The mineral assemblage is greater than 90% olivine, with minor amounts of other minerals such as pyroxene, chromite and pyrope. Dunite is the olivine-rich end-member of the peridotite group of mantle-derived rocks. Dunite and other peridotite rocks are considered the major constituents of the Earth's mantle above a depth of about 400 kilometers. Dunite is rarely found within continental rocks, but where it is found, it typically occurs at the base of ophiolite sequences where slabs of mantle rock from a subduction zone have been thrust onto continental crust by obduction during continental or island arc collisions (orogeny). It is also found in Alpine peridotite massifs that represent slivers of sub-continental mantle exposed during collisional orogeny. Dunite typically undergoes retrograde metamorphism in near-surface environments and is altered to serpentinite and soapstone. Dunite may represent the refractory residue left after the extraction of basaltic magmas in the upper mantle. This is the type of dunite found in the lowermost parts of ophiolites, Apine peridotite massifs, and xenoliths. Dunite may also form by the accumulation of olivine crystals on the floor of large basaltic or picritic magma chambers. These "cumulate" dunites typically occur in thick layers in ultramafic to mafic layered intrusions, associated with cumulate layers of wehrlite, olivine pyroxenite, harzburgite, and even chromitite (a cumulate rock consisting largely of chromite). Small layered intrusions may be of any geologic age, for example, the Triassic Palisades Sill in New York and the larger Eocene Skaergaard complex in Greenland. The largest layered mafic intrusions are tens of kilometers in size and almost all are Proterozoic in age, for example, the Stillwater igneous complex in Montana, the Muskox intrusion (Canada), and the Great Dyke (Zimbabwe). Cumulate dunite may also be found in ophiolite complexes, associated with layers of wehrlite, pyroxenite, and gabbro.
Photographed by Michael P. Klimetz
Aaheim
Nordfjord
NORWAY
Photographed by Michael P. Klimetz
Aaheim
Nordfjord
NORWAY
Photographed by Michael P. Klimetz
Aaheim
Nordfjord
NORWAY
Photographed by Michael P. Klimetz
[With Chromite]
NORTH CAROLINA
Photographed by Michael P. Klimetz
[With Chromite]
NORTH CAROLINA
Photographed by Michael P. Klimetz
[With Chromite]
NORTH CAROLINA
Photographed by Michael P. Klimetz
[With Chromite]
NORTH CAROLINA
Photographed by Michael P. Klimetz
[With Chromite]
NORTH CAROLINA
Photographed by Michael P. Klimetz
Dunite
[Weakly Serpentinized Upper Mantle with Chromite]
Twin Sisters Dunite
[Cenozoic]
Swen Larson Quarry
Twin Sister Mountains
Acme
Whatcom County
WASHINGTON
Photographed by Michael P. Klimetz
Dunite
[Weakly Serpentinized Upper Mantle with Chromite]
Twin Sisters Dunite
[Cenozoic]
Swen Larson Quarry
Twin Sister Mountains
Acme
Whatcom County
WASHINGTON
Photographed by Michael P. Klimetz
Dunite
[Weakly Serpentinized Upper Mantle with Chromite]
Twin Sisters Dunite
[Cenozoic]
Swen Larson Quarry
Twin Sister Mountains
Acme
Whatcom County
WASHINGTON
Photographed by Michael P. Klimetz
Dunite
[Upper Mantle Origin Forsterite Crystals with Kammererite and Phlogopite]
Gusdal Olivine Pit (Aheim Olivine Pit)
Amklovdalen, Vanylven
More Og Romsdal
NORWAY
Photographed by Michael P. Klimetz
Dunite
[Upper Mantle Origin Forsterite Crystals with Kammererite and Phlogopite]
Gusdal Olivine Pit (Aheim Olivine Pit)
Amklovdalen, Vanylven
More Og Romsdal
NORWAY
Photographed by Michael P. Klimetz
Dunite
[Upper Mantle Origin Forsterite Crystals with Kammererite and Phlogopite]
Gusdal Olivine Pit (Aheim Olivine Pit)
Amklovdalen, Vanylven
More Og Romsdal
NORWAY
Photographed by Michael P. Klimetz
Dunite
[Upper Mantle Origin Forsterite Crystals with Kammererite and Phlogopite]
Gusdal Olivine Pit (Aheim Olivine Pit)
Amklovdalen, Vanylven
More Og Romsdal
NORWAY
Photographed by Michael P. Klimetz
Dunite
[Upper Mantle Origin Forsterite Crystals with Kammererite and Phlogopite]
