DUNITE

 

Dunite is a >90% olivine-bearing peridotite, which is an ultramafic, intrusive igneous rock.  How did dunite get its name?  The type locality for dunite is Dun Mountain in New Zealand.  Shown below is a sample of Dun Mountain dunite.  It’s been metamorphosed, but not serpentinized.  This dunite tectonite has a grayish core of olivine plus some small black masses of chromite.  The yellow-orangish weathering rind is referred to as “dun”-colored in New Zealand.  The whole of Dun Mountain has surface-weathered dunite rocks of this color.  Broken pieces show that the unweathered olivine is grayish.

 

Dunite (4.9 cm across) from the Permian of the dunite type locality: Dun Mountain, New Zealand.

Geologic unit & age: Dun Mountain Ophiolite Belt (= suture zone between a terrane and the ancient New Zealand margin of the Gondwana supercontinent), Early Permian, 275-285 m.y.

Locality: Dun Mountain, Bryant Range, ~15 km southeast of the city of Nelson, northwest of the Pelorus River, northern South Island, central New Zealand.

 


 

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