If partial melting of the harzburgite continues, all of the pyroxene may be extracted from it to form magma, leaving behind the pyroxene-poor peridotite called dunite.
22.
The mantle parts of the lithosphere are made of harzburgite and dunite ( both peridotites ), with about 50 to 80 % of the minerals now transformed into serpentinite.
23.
It is considered equally plausible that such large dunite-peridotite bodies represent lave channels or sills through which, perhaps, great volumes of lava flowed en route to the surface.
24.
Adams'work showed that only two minerals, dunite and eclogite, could possible make up the discontinuity, and further exploration showed that dunite was a better fit than eclogite.
25.
Adams'work showed that only two minerals, dunite and eclogite, could possible make up the discontinuity, and further exploration showed that dunite was a better fit than eclogite.
26.
Nearly the entire area is underlain by dunite, a variety of peridotite consisting of dark green olivine and minor chromite, which has been partly or entirely serpentinized to antigorite magnesite-magnetite.
27.
However, serpentinite synthesis and spinel cracking reactions require hydrothermal alteration of pristine peridotite-dunite, which is a finite process intrinsically related to metamorphism, and further, requires significant addition of water.
28.
One proposed reaction is that of the olivine-rich rock dunite, or its hydrated equivalent serpentinite with carbon dioxide to form the carbonate mineral magnesite, plus silica and iron oxide ( magnetite ).
29.
Dunite was named by the German geologist, Ferdinand von Hochstetter in 1859 after Dun Mountain near oxidizes the iron in olivine in temperate climates ( weathering in tropical climates creates a deep red soil ).
30.
In all cases these rocks are pyrometamorphic ( that is, metamorphosed in the presence of molten rock ) and represent either fertile mantle ( lherzolite ) or partially depleted mantle ( harzburgite, dunite ).
