Ultramafic rock

Ultramafic Rock

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Ultramafic rock

Ultramafic (also referred to as ultrabasic) rocks are igneous and meta-igneous rocks with very low silica content (less than 45%), generally >18% Mg

Magnesium

Magnesium is a chemical element with the symbol Mg, atomic number 12, atomic weight 24.3050 and common oxidation number +2.Magnesium, an alkaline earth metal, is the ninth most abundance of the chemical elements in the universe by mass....
O

Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
, high Fe

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. Iron is a Group 8 element and period 4 element. Iron is lustrous and silvery in color....
O, low potassium

Potassium

Potassium is a chemical element. It has the symbol K , atomic number 19, and atomic mass 39.0983. Potassium was first isolated from potash, hence the name....
, and are composed of usually greater than 90% mafic

Mafic

Mafic is an adjective describing a silicate mineral or rock that is rich in magnesium and iron; the term was derived by contracting "magnesium" and "ferric"....
mineral

Mineral

A mineral is a naturally occurring solid formed through Geology processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties....
s (dark colored, high magnesium

Magnesium

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. Iron is a Group 8 element and period 4 element. Iron is lustrous and silvery in color....
content). The Earth's mantle is considered to be composed of ultramafic rocks.

Intrusive ultramafic rocks
Intrusive ultramafic rocks are often found in large, layered ultramafic intrusion

Ultramafic to mafic layered intrusions

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Intrusive ultramafic rocks

Intrusive ultramafic rocks are often found in large, layered ultramafic intrusion

Ultramafic to mafic layered intrusions

Ultramafic to mafic layered intrusions are found in typically ancient cratons and are rare but worldwide in distribution. The intrusive complexes exhibit evidence of Fractional crystallization and crystal segregation by settling or floating of minerals from a melt....
s where differentiated rock types often occur in layers. Such cumulate rock types do not represent the chemistry of the magma from which they crystallized. The ultramafic intrusives include the dunite

Dunite

Dunite is an igneous rock, plutonic 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....
s, peridotite

Peridotite

A peridotite is a dense, coarse-grained igneous rock, consisting mostly of the minerals olivine and pyroxene. Peridotite is ultramafic and ultrabasic, as the rock contains less than 45% silica....
s and pyroxenite

Pyroxenite

Pyroxenite is an ultramafic igneous Rock consisting essentially of minerals of the pyroxene group, such as augite and diopside, hypersthene, bronzite or enstatite....
s. Other rare varieties include troctolite

Troctolite

Troctolite is a rare ultramafic intrusive rock type. It consists essentially of variable amounts of olivine and calcic plagioclase along with variable minor pyroxene....
which has a greater percentage of calcic plagioclase. These grade into the anorthosite

Anorthosite

Anorthosite is a phaneritic, intrusive igneous rock characterized by a predominance of plagioclase feldspar , and a minimal mafic component . Pyroxene, ilmenite, magnetite, and olivine are the mafic minerals most commonly present....
s. Gabbro

Gabbro

Gabbro refers to a large group of dark, coarse-grained, intrusive igneous rock chemically equivalent to basalt. The rocks are Intrusive, formed when molten magma is trapped beneath the Earth's surface and cools into a crystalline mass....
and norite

Norite

Norite is a mafic intrusive igneous rock composed largely of the calcium-rich plagioclase labradorite and hypersthene with olivine. Norite is essentially indistinguishable from gabbro without thin section study under the petrographic microscope....
often occur in the upper portions of the layered ultramafic sequences. Hornblendite

Hornblendite

Hornblendite is a plutonic rock consisting mainly of the amphibole hornblende. Hornblende rich ultramafic rocks are rare and when hornblende is the dominant mineral phase they are classified as hornblendites with qualifiers such as garnet hornblendite identifying a second abundant contained mineral....
and, rarely phlogopitite are also found.

Volcanic ultramafic rocks

Volcanic ultramafic rocks are rare outside of the Archaean and are essentially restricted to the Neoproterozoic

Neoproterozoic

The Neoproterozoic Era is the unit of geologic time scale from 1,000 to 542 +/- 0.3 million years ago. The terminal Era of the formal Proterozoic Eon , it is further subdivided into the Tonian, Cryogenian, and Ediacaran Periods....
or earlier, although some boninite

Boninite

Boninite is a mafic extrusive Rock high in both magnesium and silica, formed in fore-arc environments, typically during the early stages of subduction....
lava

Lava

Lava is molten Rock expelled by a volcano during an eruption. When first expelled from a volcanic vent, it is a liquid at temperatures from 700 ?C to 1,200 ?C ....
s currently erupted within back-arc basin

Back-arc basin

Back-arc basins are geologic features, submarine basins associated with island arcs and subduction zones.They are found at some convergent boundary, presently concentrated in the Western Pacific ocean....
s (Manus Trough, Philippines

Philippines

The Philippines, officially known as the Republic of the Philippines, is a country in Southeast Asia with Manila as its capital city. It comprises 7,107 islands in the western Pacific Ocean....
) verge on being ultramafic. Subvolcanic ultramafic rocks and dykes persist longer, but are also rare. Many of the lavas being produced on Io

Io (moon)

'Io' is the innermost of the four Galilean moons natural satellite of Jupiter and, with a diameter of 3,642 Kilometre, the List of moons by diameter in the Solar System....
may be ultramafic, as evidenced by their temperature

Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater temperature....
s which are higher than terrestrial

Earth

Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...
mafic

Mafic

Mafic is an adjective describing a silicate mineral or rock that is rich in magnesium and iron; the term was derived by contracting "magnesium" and "ferric"....
eruptions.

Examples include komatiite

Komatiite

Komatiites are ultramafic mantle-derived volcanic rocks. They have low SiO2, low K2O, low Al2O3, and high to extremely high MgO....
and picritic basalt. Komatiites can be host to ore

Ore

An ore is a type of Rock that contains minerals such as gemstones and metals that can be extracted through mining and refined for use. Samples of ore in the form of exceptionally beautiful crystals, exotic layering visible when sectioned or polished or metallic presentations such as large nuggets or crystalline formations of metals suc...
deposits of nickel

Nickel

Nickel is a chemical element, with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge....
.

Ultrapotassic ultramafic rocks

Technically ultrapotassic rocks

Ultrapotassic igneous rocks

Ultrapotassic igneous rocks are a class of rare, volumetrically minor generally ultramafic or mafic silica-depleted igneous rocks.Ultrapotassic rocks are defined by molar potassium2oxygen/sodium2O >3 in much of the scientific literature....
and melilitic

Melilite

Melilite refers to a mineral of the melilite group. Minerals of the group are solid solutions of several endmembers, the most important of which are gehlenite and akermanite....
rocks are considered a separate group, based on melting model criteria, but there are ultrapotassic and highly silica-under-saturated rocks with >18% MgO. which can be considered "ultramafic".

Ultrapotassic, ultramafic igneous rocks such as lamprophyre

Lamprophyre

Lamprophyres are uncommon, small volume ultrapotassic igneous rocks igneous rocks primarily occurring as Dike , lopoliths, laccoliths, stocks and small intrusions....
, lamproite

Lamproite

Lamproites are ultrapotassic igneous rocks earth's mantle-derived igneous rock. They have low CaO, Al2O3, Na2O, high K2O/Al2O3, a relatively high MgO content and extreme enrichment in incompatible elements....
and kimberlite

Kimberlite

Kimberlite is a type of potassic volcanic rock best known for sometimes containing diamonds. It is named after the town of Kimberley, Northern Cape in South Africa, where the discovery of an diamond in 1871 spawned a diamond rush, eventually creating the Big Hole....
are known to have reached the surface of the Earth. Although no modern eruptions have been observed, analogues are preserved.

Most of these rocks occur as dikes

Dike (geology)

A dike or dyke in geology is a type of sheet intrusion referring to any geologic body that cuts discordantly across* planar wall rock structures, such as bedding or foliation...
, diatreme

Diatreme

A diatreme is a Breccia filled volcanic pipe that was formed by a gaseous explosion. Diatremes often breach the surface and produce a tuff cone or a filled relatively shallow crater known as a maar or other volcanic pipes....
s, lopolith

Lopolith

A lopolith is a large igneous intrusion which is Lenticular in shape with a depressed central region. Lopoliths are generally concordant with the intruded stratum with Dike or funnel-shaped feeder bodies below the body....
s or laccolith

Laccolith

A laccolith is an igneous Intrusion that has been injected between two layers of sedimentary rock. The pressure of the magma is high enough that the overlying strata are forced upward, giving the laccolith a dome or mushroom-like form with a generally planar base....
s, and very rarely, intrusions. Most kimberlite and lampproite occurrences occur as volcanic and subvolcanic diatremes and maar

Maar

A maar is a broad, low-relief volcanic crater that is caused by a phreatomagmatic eruption, an explosion caused by groundwater coming into contact with hot lava or magma....
s; lavas are virtually unknown.

Vents of Proterozoic

Proterozoic

The Proterozoic is a eon representing a period before the first abundant complex life on Earth. The Proterozoic Eon extended from 2500 annum to 542.0 ? 1.0 Ma , and is the most recent part of the old, informally named ?Precambrian? time....
lamproite (Argyle diamond mine

Argyle diamond mine

The Argyle diamond mine is a diamond mining located in the Kimberley region of Western Australia. The Argyle mine is the largest diamond producer in the world by volume, although due to the low proportion of gem-quality diamonds, is not the leader by value....
), and Cenozoic

Cenozoic

The Cenozoic Era...
lamproite (Gaussberg

Gaussberg

Gaussberg is an extinct Volcanoes cone, 370 metres high, fronting on Davis Sea immediately west of the Posadowsky Glacier in Kaiser Wilhelm II Land in Antarctica....
, Antarctica

Antarctica

Antarctica is Earth's southernmost continent, overlying the South Pole. It is situated in the Antarctica of the southern hemisphere, almost entirely south of the Antarctic Circle, and is surrounded by the Southern Ocean....
) are known, as are vents of Devonian

Devonian

The Devonian is a geologic period of the Paleozoic era spanning from . It is named after Devon, England, where rocks from this period were first studied....
lamprophyre (Scotland

Scotland

conventional_long_name = ScotlandAlba|common_name= Scotland|image_flag = Flag of Scotland.svg|flag_width = 130px...
). Kimberlite pipes in Canada

Canada

Canada is a country occupying most of northern North America, extending from the Atlantic Ocean in the east to the Pacific Ocean in the west and northward into the Arctic Ocean....
, Russia

Russia

Russia , or the Russian Federation , is a list of countries spanning more than one continent country extending over much of northern Eurasia....
and South Africa

South Africa

The Republic of South Africa, also known by Official names of South Africa, is a country located at the southern tip of the continent of Africa....
have incompletely-preserved tephra

Tephra

Tephra is air-fall material produced by a Volcano regardless of composition or fragment size. Tephra is typically Rhyolite in composition, as most explosive volcanoes are the product of the more viscosity felsic or high silica magmas....
and agglomerate

Agglomerate

Agglomerates are coarse accumulations of large blocks of volcano material that contain at least 75% volcanic bomb. Volcanic bombs differ from volcanic blocks in that their shape records fluidal surfaces: they may, for example, have ropy, cauliform, scoriaceous, or folded, chilled margins and spindle, spatter, ribbon, ragged, or amoeboid s...
facies

Facies

In geology, facies are a body of rock with specified characteristics. [Reading ] Ideally, a facies is a distinctive rock unit that forms under certain conditions of sedimentation, reflecting a particular process or environment....
.

These are generally diatreme

Diatreme

Volcanic ash

Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcano eruptions, less than in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact with water causing phreatomagmatic eruptions...
deposits are partially preserved. These represent low-volume

Volume

The volume of any solid, liquid, plasma, vacuum or theoretical object is how much three-dimensional space it occupies, often quantified numerically....
volatile melts and attain their ultramafic chemistry

Chemistry

Chemistry is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions....
via a different process to typical ultramafic rocks.

Carbonatite

Carbonatite

Carbonatites are intrusive or extrusive igneous Rock defined by mineralogic composition consisting of greater than 70 volume percent carbonate minerals....
s are rare high-carbonate

Carbonate

In chemistry, a carbonate is a salt or ester of carbonic acid....
, low-silica igneous rocks.

Metamorphic ultramafic rocks

Metamorphism

Metamorphism is the solid-state Crystallization of pre-existing Rock due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids....
of ultramafic rocks in the presence of water

Water

Water is a common chemical substance that is essential for the survival of all known forms of life. In typical usage, water refers only to its liquid form or States of matter, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam....
and/or carbon dioxide

Carbon dioxide

Carbon dioxide is a chemical compound composed of two oxygen atoms covalent bond to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state....
results in two main classes of metamorphic ultramafic rock; talc carbonate

Talc carbonate

Talc carbonate is a geologic term for a suite of rock and mineral compositions found in metamorphism ultramafic rocks.The term refers to the two most common end-member minerals found within ultramafic rocks which have undergone talc-carbonation or carbonation reactions, talc and the carbonate mineral magnesite....
and serpentinite

Serpentinite

Serpentinite is a Rock composed of one or more serpentine minerals. Minerals in this group are formed by serpentinization, a hydration and metamorphic rock transformation of ultramafic rock from the Earth's Mantle ....
.

Talc carbonation reactions occur in ultramafic rocks at lower greenschist

Greenschist

Greenschist - also known as greenstone - is a general field petrology term applied to metamorphic rocks and/or altered mafic volcanic rock....
through to granulite

Granulite

Granulites are fine to medium?grained metamorphic rocks that have experienced high temperatures of metamorphism, composed mainly of feldspars sometimes associated with quartz and anhydrous mafic, with granoblastic texture and gneissose to massive structure....
facies metamorphism when the rock in question is subjected to metamorphism and the metamorphic fluid has more than 10% molar proportion of carbon dioxide

Carbon dioxide

Carbon dioxide is a chemical compound composed of two oxygen atoms covalent bond to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state....
.

When the metamorphic fluids in contact with the ultramafic rock have less than 10% CO2 the metamorphic reactions favor serpentinisation reactions, resulting in chlorite

Chlorite

The chlorite ion is ClO2-. A chlorite is a compound that contains this group,with chlorine in oxidation state +3....
-serpentine

Serpentine

The serpentine group describes a group of common rock-forming hydroxy magnesium iron Silicate minerals#Phyllosilicates minerals; they may contain minor amounts of other elements including chromium, manganese, cobalt and nickel....
-amphibole

Amphibole

Amphibole defines an important group of generally dark-colored rock-forming Silicate minerals minerals, composed of double chain SiO4 tetrahedron, linked at the vertices and generally containing ions of iron and/or magnesium in their structures....
type assemblages.

Distribution in space and time

The majority of ultramafic rocks are exposed in orogenic belts, and predominate in Archaean and Proterozoic

Proterozoic

Phanerozoic

The Phanerozoic Eon is the current eon in the geologic timescale, and the one during which abundant animal life has existed. It covers roughly 545 million years and goes back to the time when diverse hard-shelled animals first appeared....
are rarer, and there are very few recognised true ultramafic lavas in the Phanerozoic.

Many surface exposures of ultramafic rocks occur in ophiolite complexes where deep mantle-derived rocks have been obducted

Obduction

Obduction is the overthrusting of continental crust by oceanic crust or mantle rocks at a destructive plate boundary. It can occur during an orogeny....
onto continental crust

Continental crust

The continental crust is the layer of igneous, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as Continental shelf....
along and above subduction

Subduction

In geology, subduction is the process that takes place at convergent boundary by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge....
zones.

Ultramafic rocks and the regolith

Where ultramafic rocks (in particular, the types which have low amounts of nutrient elements such as calcium

Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft grey alkaline earth metal, and is the fifth most abundant element by mass in the earth's Crust ....
, potassium

Potassium

Potassium is a chemical element. It has the symbol K , atomic number 19, and atomic mass 39.0983. Potassium was first isolated from potash, hence the name....
and phosphorus

Phosphorus

Phosphorus is the chemical element that has the symbol P and atomic number 15. The name comes from the and . A Valency nonmetal of the nitrogen group, phosphorus is commonly found in inorganic phosphate minerals....
) are exposed on the surface, the high metal

Metal

In chemistry, a metal is a chemical element whose atoms readily lose electrons to form positive ions , and form metallic bonds between other metal atoms and ionic bonds between nonmetal atoms....
content of the rocks creates unique vegetation

Vegetation

refers to the flora system of a specific region....
. Examples are the ultramafic woodland

Woodland

Ecologically, a woodland is an area covered in trees, usually at low density, forming an open habitat, allowing sunlight to penetrate between the trees, and limiting shade....
s and ultramafic barrens of the Appalachian mountain

Mountain

A mountain is a landform that stretches above the surrounding land in a limited area usually in the form of a peak. A mountain is generally steeper than a hill....
s and piedmont

Piedmont (disambiguation)

A piedmont is a foothill, and "piedmont" has become a generic designation for foothill regions in geography.Places and things known as Piedmont include:...
, the "wet maquis

Maquis

Maquis or 'macchia' is a type of high ground in Corsica covered in thick vegetation, where privateers used to hide. The name has been adopted by a variety of guerilla movements in francophone countries....
" of the New Caledonia rain forests

New Caledonia rain forests

The New Caledonia rain forests are a terrestrial ecoregion, located in New Caledonia in the Oceania. It is a Tropical and subtropical moist broadleaf forests ecoregion, part of the Australasia ecozone....
, and the ultramafic forest

Forest

File:Stara planina suma.jpgA forest is an area with a high density of trees. There are many definitions of a forest, based on various criteria....
s of Mount Kinabalu

Mount Kinabalu

Mount Kinabalu is a prominent mountain in Southeast Asia. It is located in Kinabalu National Park in the east Malaysian state of Sabah, which is on the island of Borneo in the tropics....
and other peaks in Sabah

Sabah

Sabah is a Malaysian States of Malaysia located on the northern portion of the island of Borneo . It is the second largest state in Malaysia after Sarawak, which it borders on its south-west....
, Malaysia

Malaysia

Malaysia is a federation that consists of States of Malaysia in Southeast Asia with a total landmass of . The capital city is Kuala Lumpur, while Putrajaya is the seat of the federal government....
. Vegetation is typically stunted, and is sometimes home to endemic

Endemic (ecology)

Endemism is the ecological state of being unique to a particular geographic location, such as a specific island, Habitat type, nation, or other defined zone....
species adapted to the metallic soil

Soil

Soil is the naturally occurring, unconsolidated or loose covering on the Earth's surface. Soil is composed of particles of broken rock that have been altered by chemical and environmental processes including weathering and erosion....
s.

Often thick, magnesite

Magnesite

Magnesite is magnesium carbonate, magnesiumcarbonoxygen3. Iron substitutes for magnesium with a complete solution series with siderite, FeCO3....
-calcrete caprock

Caprock

The Caprock is a region in the Texas Panhandle of Texas . It is the land to the west of the Caprock Escarpment, which separates it from plains stretching to the east at a much lower elevation....
, clay

Clay

Clay is a naturally occurring material composed primarily of fine-grained minerals, which show plasticity through a variable range of water content, and which can be hardened when dried and/or fired....
ey laterite

Laterite

Laterite is a surface formation in hot and wet tropical areas which is enriched in iron and aluminium and develops by intensive and long lasting weathering of the underlying parent rock....
and duricrust

Duricrust

Duricrust refers to a thin hard layer on or near the surface of soil, usually a few millimeters to a few centimeters thick.It is a general term for a zone of chemical precipitation and hardening formed at or near the surface of sedimentary rock bodies through pedogenic and non-pedogenic processes....
forms over ultramafic rocks in tropical and subtropical environments. Particular floral assemblages associated with highly nickeliferous ultramafic rocks are indicative tools for mineral exploration

Mineral exploration

Mineral exploration is the process undertaken by companies, partnerships or corporations in the endeavour of finding ore to mining. Mineral exploration is a much more intensive, organised and professional form of mineral prospecting and, though it frequently uses the services of prospecting, the process of mineral exploration on the whole is...
.

Weathered ultramafic rocks may form lateritic nickel ore deposits

Lateritic nickel ore deposits

Lateritic nickel ore deposits are surficial, weathered rinds formed on ultramafic rocks.They comprise 73% of the continental world nickel resources and will be in the future the dominant source for the winning of nickel....

Ultramafic rock

Intrusive ultramafic rocks

Volcanic ultramafic rocks

Ultrapotassic ultramafic rocks

Metamorphic ultramafic rocks

Distribution in space and time

Ultramafic rocks and the regolith

See also