Ultramafic (or ultrabasic) rocks are igneous rocks with very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium and are composed of usually greater than 90% mafic minerals (dark colored, high magnesium and iron content). The Earth's mantle is considered to be composed of ultramafic rocks. Igneous rocks are formed when molten rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... The chemical compound silicon dioxide, also known as silica, is the oxide of silicon, chemical formula SiO2. ... In geology, mafic minerals and rocks are silicate minerals, magmas, and volcanic and intrusive igneous rocks that have relatively high concentrations of the heavier elements. ... This article is about minerals in the geologic sense; for nutrient minerals see dietary mineral; for the band see Mineral (band). ... General Name, Symbol, Number magnesium, Mg, 12 Chemical series alkaline earth metals Group, Period, Block 2, 3, s Appearance silvery white Atomic mass 24. ... General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge Atomic mass 55. ... Earth cutaway from core to exosphere. ...

Intrusive Ultramafic Rocks

Intrusive ultramafic rocks are often found in large, layered ultramafic intrusions where differentiated rock types often occur in layers. Such cumulate rock types do not represent the chemistry of the magma from which they crystallised. It has been suggested that this article or section be merged with Ultramafic intrusion. ...

• Troctolite-Gabbro-Norite
• Dunite-Peridotite
• Anorthosite
• Hornblendite and, rarely phlogopitite
• Pyroxenite

Troctolite is a rare ultramafic intrusive rock type. ... Gabbro specimen. ... Norite is a mafic intrusive igneous rock composed largely of the calcium rich plagioclase labradorite and hypersthene with olivine. ... Dunite is an igneous, plutonic rock, of ultramafic composition, with coarse grained or phaneritic texture. ... Peridotite Peridotite is a dense, coarse-grained rock, consisting mostly of the minerals olivine and pyroxene. ... Anorthosite is a phaneritic, intrusive igneous rock characterized by a predominance of plagioclase feldspar (90-100%), and a minimal mafic component (0-10%). Pyroxene, ilmenite, magnetite, and olivine are the mafic minerals most commonly present. ... Pyroxenite is a rock consisting essentially of minerals of the pyroxene group, such as augite and diallage, hypersthene, bronzite or enstatite. ...

Volcanic Ultramafic Rocks

Volcanic ultramafic rocks are rare outside of the Archaean and are essentially restricted to the Neoproterozoic or earlier, although some boninite lavas verge on being ultramafic. Subvolcanic ultramafic rocks and dykes persist longer, but are also rare. Many of the lavas being produced on Io may be ultramafic, as evidenced by their temperatures which are higher than terrestrial mafic eruptions. The Archean is a geologic eon; it is a somewhat antiquated term for the time span between 2500 million years before the present and 3800 million years before the present. ... The Neoproterozoic is the geological era from 1000 Ma to 542 Ma (million years ago). ... Atmospheric characteristics Atmospheric pressure trace Sulfur dioxide 90% Io (eye-oe, IPA: , Greek Ῑώ) is the innermost of the four Galilean moons of Jupiter. ... In geology, mafic minerals and rocks are silicate minerals, magmas, and volcanic and intrusive igneous rocks that have relatively high concentrations of the heavier elements. ...

• komatiite
• Picritic basalt

Komatiites are ultramafic mantle-derived volcanic rocks. ... Picrite is an intrusive and extrusive igneous rock. ...

Ultrapotassic ultramafic rocks

Technically ultrapotassic rocks and melilitic rocks are considered a separate group, based on melting model criteria, but there are ultrapotassic and highly silica-undersaturated rocks with >18% MgO. which can be considered "ultramafic". Most of these rocks occur as dykes, diatremes, lopoliths or laccoliths, and very rarely, intrusions. Most Kimberlite and Lampproite occurrences are as volcanic and subvolcanic diatremes and maars; lavas are virtually unknown.

• Kimberlite
• Lamproite
• Lamprophyre
• Carbonatite

Hewn kimberlite core sample from the James Bay Lowlands region of Northern Ontario, Canada. ... Lamproite is a peralkaline volcanic rock. ... Lamprophyres (Greek Lampros, bright, and the terminal part of the word porphyry, meaning rocks containing bright porphyritic crystals) are a group of rocks containing phenocrysts, usually of biotite and hornblende (with bright cleavage surfaces), often also of olivine and augite, but not of feldspar. ... Carbonatites are intrusive igneous rock structures with more than 50% carbonate content, many of which contain distinctive abundances of apatite, magnetite, barite, and fluorite, that may contain economic or anomalous concentrations of rare earth elements, phosphorus, niobium, uranium, thorium, copper, iron, titanium, barium, fluorine, zirconium, and other rare or incompatible...

Distribution in Space and Time

The majority of ultramafic rocks are exposed in orogenic belts, and predominate in Archaean and Proterozoic terranes. Ultramafic magmas in the Phanerozoic are rarer, and there are very few recognised true ultramafic lavas in the Phanerozoic. The Archean is a geologic eon; it is a somewhat antiquated term for the time span between 2500 million years before the present and 3800 million years before the present. ... In geology, the Proterozoic is an eon prior to the first abundant complex life on earth. ... The Phanerozoic (occasionally Phaenerozoic) Eon is the period of geologic time during which abundant animal life has existed. ...

Many surface exposures of ultramafic rocks occur in ophiolite complexes where deep mantle-derived rocks have been obducted into continental crust along and above subduction zones. Ophiolites are sections of oceanic lithosphere that have been uplifted or emplaced to be exposed within continental crustal rocks. ... Obduction is the overthrusting of continental crust by oceanic crust or mantle rocks. ... The continental crust is the layer of granitic, sedimentary and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves. ... Subduction zones mark sites of convective downwelling of the Earths lithosphere. ...

Ultramafic rocks and the regolith

Where ultramafic rocks (in particular, the types which have low amounts of nutrient elements such as calcium, potassium and phosphorus) are exposed on the surface, the high metal content of the rocks creates unique vegetation. Examples are the Ultramafic woodlands and Ultramafic barrens of the Appalachian mountains and piedmont, the "wet maquis" of the New Caledonia rain forests, and the Ultramafic forests of Mount Kinabalu and other peaks in Sabah, Malaysia. Vegetation is typically stunted, and is sometimes home to endemic species adapted to the metallic soils.
Often thick, magnesite-calcrete caprock, clayey laterite and duricrust forms over ultramafic rocks in tropical and subtropical environments. Particular floral assemblages associated with highly nickeliferous ultramaic rocks are indicative tools for mineral exploration. General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Atomic mass 40. ... General Name, Symbol, Number potassium, K, 19 Chemical series alkali metals Group, Period, Block 1, 4, s Appearance silvery white Atomic mass 39. ... This article is about the chemical element. ... The Appalachian Mountains are a system of North American mountains running from Newfoundland and Labrador, Canada to Alabama in the United States, although the northernmost mainland portion ends at the Gaspe Peninsula of Quebec. ... The New Caledonia rain forests are a terrestrial ecoregion, located in New Caledonia in the South Pacific. ... Mount Kinabalu (Malay: Gunung Kinabalu) is Southeast Asias third highest mountain, behind Hkakabo Razi in Myanmar and Puncak Jaya in Indonesia, at a height which has been given as 4095 m (13,450 ft) [1] above sea level, or also 4101m [2] from other sources. ... State motto: Sabah Maju Jaya Capital Kota Kinabalu Governor Ahmadshah Abdullah Chief Minister Hj. ... In biology and ecology endemic means exclusively native to a place or biota, in contrast to cosmopolitan or introduced. ... Laterite is a red-colored clay rich soil found in the tropics and subtropics. ... Duricrust refers to a thin hard layer on or near the surface of soil, Usually a few millimeters to a few centimeters thick. ...

Classification

Pyroxenite - Peridotite classification