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Pyroxenite

Pyroxenite is a coarse-grained, ultramafic plutonic igneous rock composed predominantly of pyroxene minerals, with less than 40% olivine and over 90% mafic minerals by volume.^[1] It features low silica content (typically under 45 wt% SiO₂) and high concentrations of iron and magnesium, resulting in dark-colored, dense varieties that form through the slow crystallization of mantle-derived magmas.^[2] Pyroxenites are classified based on the dominant pyroxene type, including orthopyroxenites (rich in orthopyroxene like hypersthene or enstatite), clinopyroxenites (dominated by clinopyroxene such as augite or diopside), and websterites (mixtures of both).^[1] Accessory minerals often include chromite, hornblende, and minor plagioclase or biotite, contributing to its holocrystalline texture.^[1] These rocks are relatively rare at the Earth's surface due to their association with deep-seated ultramafic terrains but occur as layers, veins, dikes, or discrete bodies in ophiolite complexes, layered mafic intrusions, and mantle xenoliths brought up by volcanic activity.^[3]^[2] Geologically, pyroxenites provide critical insights into mantle processes, as they represent cumulates from basaltic magmas or products of melt-rock reactions in the upper mantle.^[1] They are found in settings like the Bushveld Complex in South Africa or ophiolites in the Eastern Desert of Egypt, where they form part of oceanic crust sequences. In some cases, pyroxenites host economic deposits of chromium and nickel, underscoring their importance in resource geology.^[1]

Overview

Etymology and Definition

The term "pyroxenite" derives from "pyroxene," the primary mineral constituent, combined with the suffix "-ite," denoting a rock type in geological nomenclature. The name "pyroxene" was coined in 1796 by French mineralogist René Just Haüy from the Greek words pyr (fire) and xenos (stranger), referring to the mineral's unusual occurrence as greenish crystals in volcanic lavas. The term pyroxenite first appeared in geological literature in 1845.^[4]^[5]^[6] Pyroxenite is defined as an ultramafic, phaneritic igneous rock composed predominantly of pyroxene-group minerals, with less than 40% olivine and over 90% mafic minerals (pyroxene + olivine) by volume, and minor accessory phases such as hornblende or biotite. Pyroxenes have the general chemical formula XY(\mathrm{Si},\mathrm{Al})_2\mathrm{O}_6, where X represents larger cations like Ca^{2+}, Na^+, Fe^{2+}, or Mg^{2+}, and Y represents smaller cations such as Fe^{3+}, Al^{3+}, Fe^{2+}, or Mg^{2+}. This distinguishes pyroxenite from peridotite, which is dominated by olivine (>40% typically), and hornblendite, which is primarily composed of amphibole minerals.^[7]^[8]^[5]^[9]^[10]^[11] Pyroxenite exhibits basic characteristics of a coarse-grained, holocrystalline texture, with dark green to black coloration due to its mafic to ultramafic composition, and a high density reflecting its iron- and magnesium-rich minerals; it forms primarily in intrusive or mantle-derived settings.^[12]^[13]^[14]

Physical Properties

Pyroxenite exhibits a dark green to black coloration, resulting from the high iron and magnesium content in its dominant pyroxene minerals. The rock displays a coarse-grained, phaneritic texture characterized by interlocking pyroxene crystals, which contribute to its overall massive appearance. In hand samples from type localities such as the Bushveld Complex in South Africa, pyroxenite often shows a greasy to vitreous luster on fresh surfaces. The density of pyroxenite typically ranges from 3.2 to 3.5 g/cm³, exceeding that of most average igneous rocks due to the prevalence of dense mafic minerals like pyroxene. This elevated density aids in distinguishing pyroxenite in geophysical surveys of ultramafic intrusions. Pyroxenite possesses a hardness of 5 to 6 on the Mohs scale, primarily owing to the inherent durability of its pyroxene components, making it resistant to scratching by common tools like a knife. Pyroxenite may exhibit weak magnetism in variants containing accessory magnetite, as observed in certain layered sequences of the Bushveld Complex where magnetic susceptibility remains low, generally below 0.05 SI units. The rock's cleavage is prismatic, inherited from the pyroxene structure, featuring two prominent planes intersecting at angles of approximately 87° and 93°, which produce blocky fragments upon breaking.

Petrology

Mineral Composition

Pyroxenite is defined by its dominance of pyroxene minerals, which comprise more than 90% of the rock's volume, making it a pyroxene-rich ultramafic lithology.^[13] These primary minerals belong to two main structural groups: clinopyroxenes, such as augite and diopside with the general formula \ce{Ca(Mg,Fe)Si2O6}, and orthopyroxenes, such as hypersthene and enstatite with the formula \ce{(Mg,Fe)SiO3}.^[15] Clinopyroxenes typically form prismatic crystals with good cleavage, while orthopyroxenes exhibit similar habits but with slight variations in optic properties.^[14] Varieties like websterite feature roughly equal proportions of clinopyroxene and orthopyroxene, often exceeding 5% of each within the total pyroxene content.^[16] Subtypes are distinguished by modal proportions; for instance, clinopyroxenite contains more than 90% clinopyroxene relative to total pyroxenes, whereas orthopyroxenite contains more than 90% orthopyroxene.^[11] These proportions influence the rock's overall texture and stability under mantle conditions. Accessory minerals constitute less than 10% of pyroxenite and include olivine (\ce{(Mg,Fe)2SiO4}), up to 40% but typically much less (often <10%), in volume, along with chromite (\ce{FeCr2O4}), magnetite, rutile, and scapolite.^[13]^[14] In eclogitic pyroxenites, garnet appears as a key accessory phase, often coexisting with omphacite and other high-pressure minerals.^[17] Hornblende may occur in hybrid forms, such as hornblende pyroxenite, where amphibole reaches up to 50% but remains subordinate to pyroxenes.^[18] Pyroxenites commonly display cumulate textures, featuring euhedral to subhedral pyroxene crystals accumulated from a crystallizing magma, with intercumulus phases filling interstices. This fabric highlights the role of crystal settling in their formation, with mineral proportions directly defining the rock's subtype and structural integrity.^[19]

Chemical Composition

Pyroxenite exhibits a distinctive ultramafic bulk chemical composition dominated by ferromagnesian oxides, reflecting its mantle-derived origins. Major element analyses typically show SiO₂ contents ranging from 40 to 52 wt%, MgO from 20 to 40 wt%, and FeO (total iron as FeO) from 10 to 20 wt%, with Al₂O₃ generally below 5 wt% and CaO between 5 and 15 wt%.^[20]^[21] These values underscore the rock's low silica and high magnesian character compared to more evolved igneous rocks. Trace elements such as Cr and Ni are notably elevated, often exceeding 900 ppm for Cr and 1000–2000 ppm for Ni, consistent with derivation from primitive mantle sources.^[20]^[22] Compositional variations exist among pyroxenite subtypes, influenced by the dominant pyroxene phase. Clinopyroxenites tend to be richer in CaO (up to 15–20 wt% in some cases), owing to the calcium-bearing nature of diopside-hedenbergite solid solutions, while orthopyroxenites display higher MgO contents (often 30–40 wt%) due to the enstatite-ferrosilite composition of orthopyroxene.^[23]^[24] In comparison to peridotites, pyroxenites generally have lower MgO because they contain less olivine, which drives higher magnesia in peridotitic assemblages, but they possess higher SiO₂ and CaO from the pyroxene matrix.^[20]^[25] Whole-rock geochemical analyses of pyroxenite are commonly performed using X-ray fluorescence (XRF) spectrometry for major elements or inductively coupled plasma mass spectrometry (ICP-MS) following acid digestion, providing precise oxide weight percentages.^[23]^[22] Normative mineral mode calculations, based on these oxide data using methods like CIPW norms, help estimate the proportional contributions of pyroxene and accessory phases without direct modal analysis.^[25]

Classification and Types

Pyroxene-Based Classification

Pyroxenite classification is fundamentally mineralogical, emphasizing the dominant pyroxene type within the rock's modal composition, as outlined in the International Union of Geological Sciences (IUGS) scheme for ultramafic rocks. This framework employs a ternary diagram plotting the relative proportions of olivine (Ol), orthopyroxene (Opx), and clinopyroxene (Cpx), where pyroxenites are defined by pyroxene totals exceeding 60% and olivine below 40%, distinguishing them from peridotites. The diagram facilitates precise delineation of subtypes based on pyroxene dominance, providing a static mineralogical basis independent of textural or genetic considerations.^[26]^[19] Clinopyroxenites are characterized by a predominance of monoclinic pyroxenes, such as augite and diopside, which constitute more than 90% of the total pyroxene content. These rocks form the clinopyroxene apex of the IUGS ternary diagram, with minimal orthopyroxene or olivine contributions from accessory minerals. This composition reflects environments where calcium-rich pyroxenes crystallize abundantly, often in mantle-derived intrusions.^[26]^[19] Orthopyroxenites, in contrast, are dominated by orthorhombic pyroxenes including hypersthene and bronzite, exceeding 90% of the pyroxene fraction and occupying the orthopyroxene apex on the diagram. Such rocks highlight magnesium-rich conditions during formation, with clinopyroxene present only in trace amounts alongside minor olivine or other accessories.^[26]^[19] Websterites represent a balanced assemblage, featuring approximately equal proportions of clinopyroxene and orthopyroxene (typically 40-50% each), positioned along the central Opx-Cpx join of the ternary plot with low olivine. Subtypes include aluminous websterite, where pyroxenes incorporate elevated aluminum, leading to associated minerals like spinel or garnet, though the core classification remains tied to the pyroxene ratio. This equilibrium underscores mixed crystallization histories in ultramafic suites.^[26]^[19]

Textural and Genetic Types

Pyroxenites exhibit a range of textures that reflect their crystallization histories, primarily dominated by pyroxene minerals such as orthopyroxene, clinopyroxene, or their combinations. Cumulate textures are common, characterized by layered or adcumulate structures where pyroxene crystals accumulate with graded layering, often showing euhedral to subhedral grains of varying sizes due to sequential settling from a magma chamber.^[27] Poikilitic textures feature large, oikocrystic pyroxene crystals that enclose smaller, chadacrystic grains of olivine or plagioclase, indicating late-stage growth of the enclosing pyroxene around earlier-formed phases in a slowly cooling environment.^[28] Pegmatitic textures occur in coarser variants, typically in vein-like bodies, with exceptionally large pyroxene crystals (often exceeding several centimeters) formed under low strain and prolonged crystallization conditions.^[29] Genetic types of pyroxenites are distinguished by their formation settings, integrating textural evidence with origin. In layered intrusions, pyroxenites form as cumulate layers from the fractionation of mafic magmas, exemplified by orthopyroxenite markers in complexes like the Bushveld, where they appear as discontinuous, modally graded units within broader ultramafic sequences.^[29] Mantle xenoliths represent another primary genetic type, derived from the upper mantle and transported to the surface, often displaying equilibrated or intergrowth textures with relict high-pressure minerals like garnet, reflecting melt-peridotite interactions at depths of 50-60 km.^[30] Metamorphic segregations arise from the recrystallization and segregation of pyroxene during regional or contact metamorphism of mafic protoliths, producing coarser, sometimes poikilitic textures in association with surrounding peridotites or gabbros.^[31] Rare volcanic pyroxenites occur as aphanitic or fine-grained variants within basaltic lavas or as xenoliths, where rapid cooling limits crystal growth, though such occurrences are uncommon due to the rock's typical intrusive nature.^[30] A key distinction in pyroxenites lies between primary types, which originate directly from igneous or mantle processes with preserved magmatic minerals like fresh clinopyroxene and olivine, and secondary types resulting from metamorphic alteration, where hydrothermal fluids or solid-state recrystallization introduce secondary phases such as amphibole or chlorite without fundamentally altering the pyroxene dominance.^[27] This classification emphasizes observable textures and avoids reliance solely on mineral proportions, such as the dominance of orthopyroxene versus clinopyroxene, to differentiate practical field and petrologic groupings.^[28]

Formation and Petrogenesis

Igneous and Mantle Processes

Pyroxenites form as igneous cumulates primarily through fractional crystallization within mafic-ultramafic magma chambers, where early-formed pyroxene crystals settle due to density differences, accumulating in layered intrusions such as the Bushveld Complex or Stillwater Complex.^[32] This process involves the progressive cooling of basaltic or picritic magmas, leading to the precipitation of orthopyroxene, clinopyroxene, or both, often intergrown with minor olivine or plagioclase, resulting in adcumulate or mesocumulate textures.^[27] Gravity settling dominates in these environments, promoting the segregation of dense pyroxene-rich layers that represent a key stage in the differentiation of continental crust by removing mafic components from evolving magmas.^[33] In mantle settings, pyroxenites arise from reactions between percolating silicate melts and surrounding peridotite, where silica-rich melts dissolve olivine and precipitate pyroxene, forming veins or layers that enhance mantle heterogeneity.^[34] For instance, basaltic or komatiitic melts migrating through the lithospheric mantle at depths of 1-2 GPa interact with harzburgite, producing orthopyroxene- or clinopyroxene-dominated pyroxenites via incongruent dissolution, as exemplified in studies of Ethiopian and Kerguelen xenoliths.^[35] Under higher pressures (>4 GPa), eclogite residues or recycled crustal material can transform into garnet pyroxenites through partial melting and reaction, stabilizing dense assemblages in the deep mantle.^[36] Petrogenetic models highlight the role of these processes in crustal differentiation, where pyroxenite cumulates act as sinks for incompatible elements, influencing magma evolution and contributing to the andesitic composition of continental crust.^[37] A simplified reaction illustrating melt-peridotite interaction is:

\mathrm{Mg_2SiO_4 (olivine) + SiO_2 (melt) \rightarrow 2 MgSiO_3 (orthopyroxene)}

This metasomatic reaction, driven by silica addition from the melt, converts olivine-bearing peridotite into pyroxene-rich domains, promoting refertilization and altering the rheological properties of the mantle.^[38] Modern isotopic studies, particularly Re-Os dating of sulfides in pyroxenites, reveal ancient mantle heterogeneities, with radiogenic Os signatures indicating incorporation of recycled eclogite-derived material dating back to the Archean, as observed in orogenic peridotite suites like Lherz or Beni Bousera.^[39] These analyses confirm that pyroxenite veins preserve long-lived isotopic disequilibria, underscoring their significance in tracing melt migration and mantle convection over billions of years.^[40]

Metamorphic and Volcanic Origins

Pyroxenites of metamorphic origin arise primarily through high-grade transformations of pre-existing rocks, contrasting with the more prevalent igneous pathways by involving solid-state recrystallization and fluid-mediated alterations rather than direct magmatic crystallization. Contact metamorphism, induced by the thermal influence of shallow intrusions, converts protoliths such as carbonate-rich sediments or mafic volcanics into pyroxene-dominated rocks within narrow aureoles. This process entails the breakdown of minerals like calcite, dolomite, and clay, facilitated by heat (typically 600–800°C) and metasomatic fluids that introduce silica and remove volatiles, yielding assemblages rich in diopside or enstatite. The resulting contact-pyroxenites often exhibit granular textures and are compositionally similar to igneous varieties but distinguished by their proximity to intrusive contacts and evidence of reaction rims on relict grains.^[41] Regional metamorphism at granulite facies provides another key pathway, as seen in ancient cratonic terrains where deep-crustal conditions drive anhydrous mineral formation. In the Lewisian Complex of Scotland, pyroxenites emerge from reactions in mafic gneisses or amphibolites under temperatures exceeding 800°C and moderate pressures (6–10 kbar), where devolatilization expels H₂O and CO₂ from hydrous phases like hornblende or biotite, stabilizing pyroxene via equilibria such as hornblende + plagioclase → pyroxene + garnet + melt. Metasomatism, involving infiltration of CO₂- or H₂O-rich fluids, further modifies bulk compositions by enriching Ca and Mg, promoting pyroxene nucleation and growth. Trace element patterns in clinopyroxenes from these Lewisian pyroxenites, including elevated light rare earth elements, support segregation from surrounding gneisses during prograde metamorphism, highlighting their secondary, non-magmatic derivation.^[42]^[43] Volcanic pyroxenites, though exceedingly rare, form as extrusive equivalents of ultramafic magmas in high-temperature eruptive settings, primarily within Archaean greenstone belts where komatiitic or high-Mg basaltic lavas dominate. These rocks originate from mantle-derived melts erupted at temperatures above 1400°C, which upon surface exposure undergo extreme supercooling, suppressing nucleation and favoring rapid dendritic growth of pyroxene. The hallmark spinifex texture—interlocking blades or plates of orthopyroxene or clinopyroxene—results from this disequilibrium crystallization, where constitutional undercooling at the melt-crystal interface drives skeletal habits and incomplete solidification, often leaving interstitial glass or fine-grained matrix.^[44] In the Gullewa region of Australia's Murchison Province, komatiitic pyroxenite flows exemplify this, with spinifex zones up to several meters thick attesting to thin, turbulent flows that cooled in hours to days.^[45] Such rapid quenching contrasts with slower intrusive cooling, preserving metastable textures and limiting accessory minerals like olivine to relict cores.

Occurrence

Global Distribution

Pyroxenite occurs worldwide in association with specific tectonic settings, primarily ophiolites, layered mafic intrusions of Archaean to Proterozoic age, and mantle xenoliths entrained in kimberlites. These rocks are commonly found within supra-subduction zone environments, such as ophiolitic sequences representing ancient oceanic crust, and in continental settings like cratonic lithospheres where they form as cumulates or reaction products in layered intrusions. Additionally, pyroxenites appear in orogenic massifs and as xenoliths in volcanic rocks from hotspots and arcs, reflecting melt-peridotite interactions in the upper mantle. Global compilations indicate occurrences across 55 regions and 121 localities, with notable concentrations in Alpine-Apennine ophiolites and African-European massifs.^[46]^[47]^[27] The age distribution of pyroxenite is skewed toward the Precambrian, with significant occurrences in greenstone belts dating to approximately 2.5 Ga, such as those in the Barberton region of South Africa (3.3–3.5 Ga) and the Isua supracrustal belt in Greenland (ca. 3.8 Ga). These ancient formations host ophiolite-like sequences containing pyroxenites formed during early Earth tectonic processes. Examples include Neoproterozoic ophiolites in the Eastern Desert of Egypt (Precambrian) and Cenozoic arcs like the Andes (Phanerozoic), where pyroxenites record recent mantle recycling. Isotopic dating, including Lu-Hf and Re-Os systems, confirms Proterozoic to Archaean dominance, with model ages up to 3 Ga in some cratonic xenoliths.^[48]^[46]^[49] In the mantle, it represents 2–5% of the upper mantle globally, though proportions can reach up to 10% in specific lithospheric sections, such as those beneath cratons or in delaminated arc roots. These estimates derive from petrological modeling and xenolith studies, highlighting pyroxenite's role in mantle heterogeneity without dominating overall composition.^[47] Pyroxenite distribution is closely tied to cratons and orogenic belts, with patterns mapped through geochemical databases like GEOROC, which compiles analyses from thousands of global samples to reveal spatial associations with stable continental interiors and convergent margins. Such resources facilitate tracking occurrences from Archaean shields in Africa and Australia to Phanerozoic belts in the Mediterranean and circum-Pacific regions, underscoring pyroxenite's persistence across Earth's tectonic evolution.^[50]^[46]

Notable Localities

Pyroxenite exposures in the Bushveld Complex of South Africa occur within the world's largest layered igneous intrusion, spanning over 66,000 km², where layers such as the Upper Group 1 (UG1) consist of orthopyroxenite and host major platinum-group element (PGE) ores associated with chromitite seams.^[51] These pyroxenite layers formed as part of the Rustenburg Layered Suite, dated to approximately 2.06 Ga based on U-Pb zircon geochronology.^[52] In the Great Dyke of Zimbabwe, a tabular, linear ultramafic-mafic intrusion extending 550 km, bronzite pyroxenites dominate the lower portions, interlayered with chromitite seams that contribute to economic chromium and nickel deposits.^[53] The intrusion, emplaced at 2.575 Ga into Archaean greenstones, features cyclic layering with pyroxenite units up to several meters thick, reflecting fractional crystallization processes.^[54] The Shetland Islands in the United Kingdom preserve ophiolitic pyroxenites within thrust sheets of the Shetland Ophiolite Complex, forming part of gabbro-peridotite sequences that represent ancient oceanic crust and upper mantle.^[55] These pyroxenites, including wehrlites and orthopyroxenites, occur as cumulates in the mantle section, variably serpentinized and associated with dunites and harzburgites in the eastern Unst and Fetlar areas. Along the Appalachian belt in North Carolina, USA, pyroxenites appear as segregations within the Webster-Addie ultramafic ring complex, a 10 km by 5 km elliptical body composed primarily of mantle-derived websterites and enstatite pyroxenites intruded into gneisses.^[56] Isotopic data indicate these websterites originated from subcontinental mantle sources, with clinopyroxene-rich varieties showing enrichment in light rare earth elements consistent with partial melting of depleted peridotite.^[57] The Gullewa Greenstone Belt in Western Australia hosts rare volcanic pyroxenite lavas within Archaean komatiitic sequences of the Murchison Province, exhibiting pyroxene spinifex textures indicative of high-temperature extrusion.^[58] These lavas, part of the 2.7 Ga greenstone belt, represent unusual ultramafic differentiates from komatiite magmas, closely associated with mafic volcanics in the supracrustal pile.^[59]

Significance

Geological Role

Pyroxenites play a crucial role in mantle dynamics by providing density contrasts that influence convective processes. With densities around 3.5 g/cm³, eclogitic pyroxenites are denser than surrounding peridotitic mantle (approximately 3.2–3.3 g/cm³), creating a ~1% density anomaly that promotes accumulation in the lower mantle and affects plume formation and slab stagnation.^[60] This contrast drives gravitational instabilities, such as the foundering of arc roots, where pyroxenite layers enhance sinking rates during convection.^[61] Additionally, pyroxenite lenses within the mantle, often 10–100 m thick, facilitate focused melt extraction due to their lower solidus temperatures compared to peridotite at pressures below 3.5 GPa, leading to higher melt productivities and channeling of melts toward the surface.^[47] In magma genesis, pyroxenites serve as key sources or intermediates for basalt production through partial melting. Their mafic compositions yield melts with elevated FeO/CaO ratios relative to peridotite-derived basalts, contributing up to 40% of mid-ocean ridge basalt (MORB) volumes and influencing ocean island basalt (OIB) diversity, as seen in continental OIBs where pyroxenite melting aligns with FC3MS values exceeding 0.65.^[62] Partial melting extents for pyroxenites can reach 49–92 wt% at 1450°C, far surpassing peridotite's 16–24 wt%, thereby controlling crustal thickness variations, such as the 20 km observed at Iceland.^[47] In plume-ridge interactions, pyroxenites enhance melt output in regions like Iceland, where 8–55% pyroxenite fractions in the mantle source account for geochemical heterogeneities and elevated crustal production along spreading centers.^[47] Pyroxenites act as tectonic indicators, revealing past geodynamic events. Pyroxenites formed in the mantle wedge preserve signatures of ancient subduction, with Zn/Fe ratios >12 in associated arc magmas signaling their melting in thickened mantle wedges (>40 km crust), as evidenced in modern arcs.^[63] Conversely, cumulate pyroxenite intrusions in supra-subduction zone settings mark rifting phases, crystallizing from low-Ti basaltic or boninitic magmas during lithospheric extension, as observed in Neoproterozoic ophiolites.^[27] Modern research highlights gaps in linking pyroxenite to mantle tomography via seismic velocities. Tomography models reveal slow anomalies widening to 2000–3000 km below 800 km, attributed to pyroxenite phase transitions (e.g., garnet to perovskite), which alter velocities by ~2% and buoyancy, explaining "fat plumes" and stagnant slabs.^[64] However, uncertainties in high-pressure rheology limit precise velocity-to-composition inversions, necessitating advanced deformation experiments to refine tomographic interpretations of pyroxenite distributions.^[64]

Economic Importance

Pyroxenite serves as a host rock for economically significant mineral deposits, particularly in layered ultramafic-mafic intrusions where it contains chromite, platinum-group elements (PGE), and nickel. In the Bushveld Complex of South Africa, pyroxenite layers within the Upper Critical Zone, such as the UG2 chromitite reef, host substantial PGE and chromite resources, with associated nickel sulfides.^[51] As of 2023, annual platinum production from these Bushveld pyroxenite-associated deposits is approximately 120 metric tons, representing about 70% of global supply.^[65] Similar associations occur in other intrusions like the Stillwater Complex in the United States, where pyroxenite horizons contribute to PGE and nickel extraction as byproducts of broader ultramafic mining.^[66] Beyond ore hosting, pyroxenite finds industrial applications due to its mineral composition and physical properties. It is used as a flux in iron and steel metallurgy, where its high magnesium content aids slag formation and impurity removal in blast furnaces.^[67] Additionally, crushed pyroxenite serves as a durable aggregate in construction, particularly for high-strength concrete in infrastructure projects, owing to its resistance to weathering.^[68] Exploration for pyroxenite-hosted resources relies on its distinct geophysical signatures, including high density (typically 3.0–3.3 g/cm³), which produces strong gravity anomalies detectable via surveys.^[69] However, mining operations in sulfide-bearing pyroxenites can generate acid mine drainage from pyrite oxidation, leading to environmental concerns such as water contamination with heavy metals.^[70] Despite these values, pyroxenite rarely forms primary economic targets; it is predominantly extracted as a byproduct during peridotite or gabbro mining, with no major standalone deposits reported globally.^[71]

References

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Petrology and Geochemistry of Pyroxenites from the Cabo Ortegal ...
The major element compositions of type 1, 2 and 3 pyroxenites are intermediate between those of the Cabo Ortegal peridotites and of the garnet-rich mafic layer.
[26]
[PDF] geochemistry and mineral chemistry of ultramafic rocks from the ...
The main components, CaO (19.1-24.7 wt%) and MgO (15.7-19.6 wt%), show a considerable variability, as do FeO (2.25-3.85 wt%) and Cr2O3 (0.85-1.7 wt%). Contents ...
[27]
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2024GC011686
[28]
Petrology and Geochemistry of Ophiolitic Pyroxenite in the Eastern ...
Mar 5, 2025 · Pyroxenites are an uncommon class of rocks dominated by the pyroxene group minerals. They are known to occur both in the crust and mantle of the ...
[29]
Clinopyroxenite generation via high-pressure crystallization of a ...
Their origin can be attributed to different magmatic or metamorphic processes or a combination of them. Several mantle pyroxenites are believed to result from ...
[30]
Origin of the Pegmatitic Pyroxenite in the Merensky Unit, Bushveld ...
The genesis of the pegmatitic pyroxenite that often forms the base of the Merensky Unit in the Bushveld Complex is re-examined.<|control11|><|separator|>
[31]
Pyroxenite xenoliths from the Rio Puerco volcanic field, New Mexico
Mar 2, 2017 · Mantle xenoliths have long been used to document the composition, physical properties, and tectonic evolution of the subcontinental lithosphere ...
[32]
[PDF] The textures and genesis of metamorphic pyroxene in the Freetown ...
Many pyroxene-troctolites show late pyroxene growth as: (1) elongated and flattened growths of augite which cut obliquely across layer- ing defined by olivine- ...
[33]
Cumulates rocks - ALEX STREKEISEN
Igneous rocks formed by sedimentation are termed cumulates (Latin "cumulus", a heap), and characteristically display cumulate textures.
[34]
Garnet Pyroxenite Cumulates from Cretaceous Alkaline Intraplate ...
Abstract. The elemental and isotopic properties of garnet pyroxenites can yield information on lithospheric mantle composition, thermal state, and evolutio.Garnet Pyroxenite Cumulates... · Garnet Pyroxenite Mineralogy... · Isotopic Composition Of The...
[35]
Depth-dependent peridotite-melt interaction and the origin ... - Nature
Feb 17, 2021 · Reaction between highly magnesian melt (komatiite) and peridotite leads to orthopyroxene crystallisation, yielding silica-rich harzburgite.
[36]
Melt–rock interactions in a veined mantle: pyroxenite–peridotite ...
Feb 16, 2022 · Interaction between pyroxenite melts and peridotite creates orthopyroxene-rich zones, websterites, and dunite, modifying mineralogy and ...
[37]
Fate of Pyroxenite-derived Melts in the Peridotitic Mantle
Also, our study shows that the ability of pyroxenite-derived melts to migrate through the mantle depends on the melting degree of the surrounding peridotite.
[38]
Arc-related Alaskan type magmatism: evidence from pyroxenites ...
Jan 30, 2024 · Pyroxenites of the Pakkanadu alkaline-ultramafic complex contain primarily clinopyroxenes and amphiboles with minor accessory phases like Fe- ...
[39]
Variation of modal amounts of olivine and orthopyroxene in the ...
... olivine and can be described by the following equation: MgFe2SiO4 + SiO2 → MgFe2SiO6. Mantle peridotites from the Kaapvaal and Tanzania cratons studied in ...
[40]
From crustal protoliths to mantle garnet pyroxenites: insights from Os ...
Aug 1, 2025 · Recycled pyroxenites are a key component of mantle heterogeneity, influencing magma generation and contributing to the radiogenic Os ...
[41]
Re–Os and Lu–Hf Isotope Constraints on the Origin and Age of ...
Pyroxenite layers within orogenic peridotite massifs provide direct evidence of mantle heterogeneity ... Although the Os isotopic compositions of the Beni ...
[42]
None
### Summary of Pyroxenite Formation Through Contact Metamorphism
[43]
insights into light rare earth element mobility during granulite facies ...
Feb 1, 2012 · ... Lewisian granulite complex, NW Scotland, have distinctive chemistries suggestive of different origins. Clinopyroxenes in the layered pyroxenites ...
[44]
Seeing through metamorphic overprints in Archean granulites ...
Aug 1, 2022 · The Lewisian Complex of northwest (NW) Scotland comprises a sequence of Archean igneous rocks, which have undergone a series of metamorphic ...
[45]
A global review of Hf-Nd isotopes: New perspectives on the chicken ...
Oct 20, 2022 · This review provides (1) an exhaustive compilation of Hf-Nd isotope data on peridotites and pyroxenites, (2) an overview of the isotopic ...
[46]
The role of pyroxenite in basalt genesis: Melt‐PX, a ... - AGU Journals
Jul 16, 2016 · Melt-PX predicts the melting behavior of pyroxenites as a function of P, T, and X At P > ~3.5 GPa, a large fraction (>20%) of natural ...
[47]
(PDF) Precambrian Greenstone Belts Host Different Ophiolite Types
We use in this study the new description and classification of ophiolites in order to identify potential ophiolite complexes in four Precambrian greenstone ...
[48]
Pyroxenite melting at subduction zones | Geology - GeoScienceWorld
Feb 10, 2023 · Using the GEOROC database (https://georoc.eu/) supplemented by published samples from the Andean arc, we compiled whole-rock compositions of ...Missing: occurrences | Show results with:occurrences
[49]
Pyroxenites from mantle section of Voykar Ophiolite – Melt/peridotite ...
Pyroxenites, comprising only approximately 2 %–10 % by volume of the upper mantle, are among the most important lithological heterogeneity in the mantle. The ...
[50]
GEOROC Database
The GEOROC Database (Geochemistry of Rocks of the Oceans and Continents) is a comprehensive collection of published analyses of igneous and metamorphic rocks ...GEOROC Compilation · Contribute to GEOROC · Geochemical Rock Database...
[51]
Bushveld Complex - PorterGeo Database - Ore Deposit Description
Jul 22, 2019 · Precise U-Pb zircon dating of Kwaggasnek Formation felsites gives an age of 2059.9±1 Ma, consistently younger than the main layered mafic stage ...
[52]
U–Pb geochronology documents out-of-sequence emplacement of ...
Nov 14, 2016 · In the northern lobe of the Bushveld Complex, pyroxenite intrusions that host the PGE deposits of the Platreef, and are correlated with the ...
[53]
The Great Dyke - PorterGeo Database - Ore Deposit Description
Nov 12, 2012 · The Great Dyke intruded at 2575.4±0.7 Ma into Archaean granites and greenstone belts of the Zimbabwe Craton in central Zimbabwe.<|separator|>
[54]
[PDF] The Source of the Great Dyke, Zimbabwe, and Its ... - UQ eSpace
ABSTRACT. Re-Os data for chromite separates from 10 massive chromitite seams sampled along the 550-km length of the 2.58-. Ga Great Dyke layered igneous ...
[55]
An overview of the PGE concentrations in the Shetland ophiolite ...
High-level wehrlites and pyroxenites within the gabbro unit, representing late ultramafic differentiates, contain lower levels of PGE of up to 310 ppb Pt + Pd.
[56]
The webster-addie ultramafic ring, Jackson County, North Carolina ...
Jul 6, 2018 · The mineralogy of the dunite, websterite, and enstatite pyroxenite is discussed. A table is presented showing that the Fe2SiO4 content of ...
[57]
Isotopic constraints on the origin of Appalachian mafic complexes
Aug 6, 2025 · From these isotopic results we infer that Appalachian mafic rocks have diverse origins: some are continental intrusives (BMC), others are ...
[58]
[PDF] Precambrian geology and mineral deposits (Plate 1) - NET
GULLEWA GREENSTONE BELT. MUGGA MUGGA HILL. Abb. 3. Agr. Ps. REFERENCE. All rocks ... 100 Plain Street, Perth, Western Australia. Printed by Mercury-Walch ...
[59]
[PDF] Komatiite-hosted nickel sulphide deposits, Australia
Komatiite volcanology. Regionally correlatable komatiite sequences characterise Archaean greenstone belt stratigraphy in the Yilgarn Block of Western. Australia ...Missing: Gullewa | Show results with:Gullewa
[60]
[PDF] Genesis, Preservation and Destruction of Mantle Heterogeneity
... density contrast ︎ρ = 100 kg m−3. The blue circle represents the thickness ... The gold band represents the range of thickness of pyroxenite bands ...
[61]
[PDF] Gravitational instability of magmatic arc roots - Geosciences |
Sep 10, 2014 · where (ρpy – ρm) is the density contrast between pyroxenite and mantle, Ar is the cross-sectional area of the root, and Rr is the rate of root ...
[62]
Can we identify source lithology of basalt? | Scientific Reports - Nature
May 16, 2013 · From compositional perspective, pyroxenite and peridotite generally have <30 wt% and >30 wt% MgO, respectively, see discussions in Supplementary ...Results · Fc3ms Value Can Identify... · Peridotite Melts Cannot...
[63]
Pyroxenite melting at subduction zones - GeoScienceWorld
Feb 10, 2023 · Pyroxenites, with lower solidi temperatures, play a significant role in magma generation at subduction zones, especially with thicker crusts, ...
[64]
Pyroxenite causes fat plumes and stagnant slabs - AGU Journals
Apr 27, 2017 · The average seismic velocity anomaly revealed by tomography is ~2% in the mantle (see SI for additional details), and Figures 3c and 3f thus ...
[65]
The Platinum Group Element Deposits of the Bushveld Complex in ...
Aug 6, 2025 · For comparison, annual production of platinum from the Bushveld Complex currently is only around 5 million oz. The distinction between ...
[66]
[PDF] Platinum-Group Elements in Southern Africa—Mineral Inventory and ...
Histogram showing annual production of platinum-group elements in South Africa from ... of the Bushveld Complex in South Africa: Platinum Metals. Review, v ...
[67]
Pyroxenite Market - Reports and Data
The single most significant driver of pyroxenite demand is its adoption in iron and steel metallurgy as a fluxing material. Fluxes are added to blast ...
[68]
https://www.emergenresearch.com/industry-report/pyroxenite-market
[69]
Pyroxenite Market Growth Analysis - Size and Forecast 2025-2029
Its use extends to pyroxenite in advanced refractory materials and construction, where it serves as pyroxenite as a high-grade construction aggregate.
[70]
[PDF] A gravity and magnetic study of the Skalkaho pyroxenite-syenite ...
In the modeling process, the pyroxenite core was delineated with respect to the out-lying syenites and host rocks. The mid-Creteceous Skalkaho Complex intruded ...
[71]
[PDF] Technical Document: Acid Mine Drainage Prediction - EPA
In addition to the acid contribution to surface waters, AMD may cause metals such as arsenic, cadmium, copper, silver, and zinc to leach from mine wastes.Missing: pyroxenite | Show results with:pyroxenite
[72]
Cobalt and nickel distribution and controlling factors in the Bushveld ...
This study aims to characterize Co and Ni distribution in olivine, pyroxenes, chromite, and whole rocks from different seams of the Bushveld Complex and to ...