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 ̉dunÓ-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.