Harzburgite

Harzburgite
Igneous rock
	Harzburgite from a small intrusion 35 km south of Ambositra, Madagascar
Composition
	Mostly olivine and low-calcium (CA) pyroxene

Harzburgite, an

Harz Mountains of Germany. It commonly contains a few percent chromium-rich spinel as an accessory mineral. Garnet-bearing harzburgite is much less common, found most commonly as xenoliths in kimberlite

.

Harzburgite typically forms by the extraction of partial melts from the more pyroxene-rich peridotite called lherzolite. The molten magma extracted from harzburgite may then erupt on the surface as basalt. 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. Harzburgite may also form by the accumulation of olivine and low-Ca pyroxene in large magma chambers of basalt deep in continental crust (layered intrusions).

Occurrence

Harzburgite is the most commonly found variety of peridotite in

Semail Ophiolite in Oman, the Coast Range ophiolites of California, and the Bay of Islands Ophiolite in Newfoundland

.

Harzburgite may also be found in some

Pyrenees Mountains), the Lanzo Massif in northern Italy, and the Horoman Massif

in Japan.

Garnet-bearing harzburgite is found as xenoliths in some kimberlite pipes, which are found almost exclusively in ancient continental cratons of Archean or Paleoproterozoic age. The mantle lithosphere under these cratons is particularly thick (up to 200 km or more) and cool. Garnet harzburgites are less depleted in the basalt component than most ophiolite harzburgites. Garnet harzburgite xenoliths from kimberlites in South Africa have been particularly well-characterized.

kilobars (0.5 GPa, or 5000x atmospheric pressure), olivine and low-Ca pyroxene (enstatite or bronzite) may crystallize together from normal basalt magmas to form harzburgite. These conditions were common in some layered mafic intrusions, most of which are Proterozoic in age, which formed from enormous sill-like intrusions of basalt into lower continental crust. The classic example of a Proterozoic layered intrusion with cumulate harzburgite is the Stillwater igneous complex of Montana, U.S.A. It is also found in the Bushveld Igneous Complex

, a large layered intrusion in South Africa.

References

Blatt, Harvey and Robert J. Tracy, 1996, Petrology: Igneous, Sedimentary and Metamorphic, 2nd ed., Freeman,
ISBN 0-7167-2438-3

v t e Types of rocks
Igneous rock	Adakite Andesite Alkali feldspar granite Anorthosite Aplite Basalt Basaltic trachyandesite Mugearite Shoshonite Basanite Blairmorite Boninite Carbonatite Charnockite Enderbite Dacite Diabase Diorite Napoleonite Dunite Essexite Foidolite Gabbro Granite Granodiorite Granophyre Harzburgite Hornblendite Hyaloclastite Icelandite Ignimbrite Ijolite Kimberlite Komatiite Lamproite Lamprophyre Latite Lherzolite Monzogranite Monzonite Nepheline syenite Nephelinite Norite Obsidian Pegmatite Peridotite Phonolite Phonotephrite Picrite Porphyry Pumice Pyroxenite Quartz diorite Quartz monzonite Quartzolite Rhyodacite Rhyolite Comendite Pantellerite Scoria Shonkinite Sovite Syenite Tachylyte Tephriphonolite Tephrite Tonalite Trachyandesite Benmoreite Trachybasalt Hawaiite Trachyte Troctolite Trondhjemite Tuff Websterite Wehrlite
Sedimentary rock	Argillite Arkose Banded iron formation Breccia Calcarenite Chalk Chert Claystone Coal Conglomerate Coquina Diamictite Diatomite Dolomite Evaporite Flint Geyserite Greywacke Gritstone Itacolumite Jaspillite Laterite Lignite Limestone Lumachelle Marl Mudstone Oil shale Oolite Phosphorite Sandstone Shale Siltstone Sylvinite Tillite Travertine Tufa Turbidite Varve Wackestone
Metamorphic rock	Anthracite Amphibolite Blueschist Cataclasite Eclogite Gneiss Granulite Greenschist Hornfels Calcflinta Itabirite Litchfieldite Marble Migmatite Mylonite Metapelite Metapsammite Phyllite Pseudotachylite Quartzite Schist Serpentinite Skarn Slate Suevite Talc carbonate Soapstone Tectonite Whiteschist
Specific varieties	Adamellite Appinite Aphanite Borolanite Blue Granite Epidosite Felsite Flint Ganister Gossan Hyaloclastite Ijolite Jadeitite Jasperoid Kenyte Lapis lazuli Larvikite Litchfieldite Llanite Luxullianite Mangerite Novaculite Pietersite Pyrolite Rapakivi granite Rhomb porphyry Rodingite Shonkinite Taconite Tachylite Teschenite Theralite Unakite Variolite Wad