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Gabbro

Gabbro is a dark-colored, coarse-grained (phaneritic) intrusive igneous rock with a mafic composition, formed by the slow crystallization of iron- and magnesium-rich magma deep within the Earth's crust or upper mantle.^[1] It is characterized by visible interlocking crystals, typically ranging from a few millimeters to centimeters in size, resulting from prolonged cooling over thousands to millions of years.^[2] The primary minerals in gabbro include calcium-rich plagioclase feldspar (often making up 50-75% of the rock), clinopyroxene, and olivine, with minor amounts of orthopyroxene, amphibole, or magnetite.^[3]^[4] The term "gabbro" originates from the Italian word for a type of coarse-grained igneous rock used in Tuscany, and was introduced into geological terminology by Christian Leopold von Buch in 1809.^[5] Gabbro commonly occurs in large plutonic bodies such as batholiths, layered intrusions, and ophiolite complexes, often associated with tectonic settings like subduction zones or mid-ocean ridges.^[6] Notable examples include the Bushveld Complex in South Africa^[1] and exposures in the Appalachian Mountains of the United States.^[7] Due to its durability and dark appearance, gabbro is used as a dimension stone for construction, countertops, and monuments, while its mineral content makes it a potential source for metals like nickel, chromium, and platinum.^[3] Gabbro's fine-grained equivalent is basalt,^[4] and variations like norite or troctolite reflect slight differences in mineral proportions.^[8]

Overview

Definition and Characteristics

Gabbro is a coarse-grained, mafic intrusive igneous rock formed from the slow crystallization of magma at depth within the Earth's crust. It is chemically equivalent to the extrusive rock basalt, possessing a similar overall composition but developing larger, visible crystals due to the prolonged cooling process underground.^[9]^[10] This rock displays a phaneritic texture, featuring interlocking crystals observable to the naked eye, and typically appears dark in color, ranging from black to dark green or gray. Gabbro has a density of approximately 3.0 g/cm³ (with a typical range of 2.7–3.3 g/cm³) and a hardness of 6–7 on the Mohs scale, contributing to its durability.^[10]^[11]^[12] Chemically, gabbro is characterized by low silica content (45–52 wt%) and elevated levels of iron and magnesium, with ferromagnesian minerals forming the primary components. As a key element of oceanic crust, gabbro dominates the deeper layers beneath the basaltic surface, forming through magmatic processes at mid-ocean ridges.^[10]^[13]^[9]

Etymology

The term "gabbro" originates from the Italian word of the same spelling, referring to a type of dark, coarse-grained rock found in the vicinity of the village of Gabbro near Rosignano Marittimo in Tuscany, Italy.^[14] The name was first documented in geological literature by Italian geologist Giovanni Targioni Tozzetti in 1768, who applied it to rocks observed in the Apennine Mountains' ophiolites.^[15] This early usage marked the initial recognition of gabbro as a distinct rock type among mafic intrusives. In 1809, German geologist Christian Leopold von Buch refined and formalized the term in scientific nomenclature, establishing gabbro as a specific lithology within German geology and distinguishing it from similar dark rocks.^[5] Von Buch's work helped clarify its plutonic nature, drawing from Italian field observations to integrate it into broader European petrological frameworks. The etymology of the Italian "gabbro" itself may trace back to Latin glaber, meaning "smooth" or "bare," possibly alluding to the rock's polished appearance in outcrops or its use in local stoneworking.^[5] The terminology evolved amid early confusions with other dark intrusive rocks, such as diabase (or dolerite), which shares a similar mafic composition but finer grain size; these overlaps persisted in 19th-century descriptions before clearer textural distinctions emerged.^[16] By the mid-19th century, "gabbro" had been adopted into English geological texts, reflecting its growing international use in describing coarse-grained equivalents of basalt. Older literature occasionally employed variants like "gabbroitic" to describe related textures or compositions.^[5]

Petrology

Mineral Composition

Gabbro is characterized by a mineral assemblage dominated by plagioclase feldspar and pyroxene minerals, which together constitute the majority of its volume and impart its mafic nature. The primary plagioclase is calcic, ranging from labradorite (An50-70) to bytownite (An70-90), typically comprising 40-60% of the modal composition.^[17]^[18] Clinopyroxene, most commonly augite, forms the next abundant phase at 20-40%, while orthopyroxene, such as hypersthene, is present in 10-20% in many variants, contributing to the rock's ferromagnesian content.^[19] Olivine appears in some gabbros, reaching up to 20% in olivine-rich varieties like troctolitic gabbro, often as euhedral crystals.^[20] Accessory minerals include opaque oxides like magnetite and ilmenite, which can constitute several percent and influence the rock's magnetic properties, along with apatite and trace amounts of amphibole or biotite.^[21] These minor phases fill interstices and reflect late-stage crystallization. The modal composition of gabbro emphasizes its mafic character, with high concentrations of calcium (from plagioclase), iron, and magnesium (from pyroxenes and olivine), coupled with relatively low sodium, potassium, and silica compared to more felsic rocks; this results in SiO₂ contents typically below 52 wt% and elevated FeO + MgO.^[14]^[22] A distinctive textural feature of gabbro is its ophitic texture, where larger pyroxene crystals partially or fully enclose laths of plagioclase, indicating that pyroxene crystallized after the onset of plagioclase nucleation but before its complete growth.^[23] This intergrowth reflects the slow cooling rates in plutonic environments and enhances the rock's interlocking crystalline structure.

Classification

Gabbro is classified as a plutonic igneous rock within the mafic compositional range using the QAPF modal classification diagram, recommended by the International Union of Geological Sciences (IUGS), which plots the relative proportions of quartz (Q), alkali feldspar (A), plagioclase (P), and feldspathoid (F) plus mafic minerals. In this scheme, gabbro occupies field 10 of the diagram, characterized by 0-5% quartz, 0-10% alkali feldspar, 50-90% plagioclase, and 10-50% mafic minerals (predominantly clinopyroxene), with the total light-colored minerals (Q + A + P) exceeding 10% but less than 90%. This modal approach emphasizes the rock's mineral assemblage, where calcic plagioclase (typically labradorite or bytownite, An50-An100) dominates over pyroxene, distinguishing it from more felsic rocks. The IUGS further subdivides gabbroic rocks based on the dominant mafic phases within the QAPF field 10 framework, prioritizing the ratio of plagioclase to pyroxene and the type of pyroxene present. Standard gabbro features plagioclase exceeding pyroxene in volume, with clinopyroxene (often augite) as the primary mafic mineral; in contrast, norite substitutes orthopyroxene (hypersthene or enstatite) as the dominant mafic phase, while gabbronorite exhibits roughly equal proportions of clinopyroxene and orthopyroxene. Variants such as olivine gabbro incorporate 5-85% olivine alongside these minerals, but the core distinction relies on pyroxene mineralogy rather than accessory phases like hornblende or oxides. Chemical classification of gabbro supplements modal schemes through the total alkali-silica (TAS) diagram, adapted for plutonic equivalents of volcanic rocks, which plots silica content against total alkalis (Na₂O + K₂O in wt%). Gabbro typically falls within the subalkaline gabbro field, with SiO₂ ranging from 45-52 wt% and total alkalis below the alkaline-subalkaline boundary (approximately 3-5 wt% at those silica levels), encompassing both tholeiitic and calc-alkaline series based on further discrimination like the K₂O-SiO₂ plot. This chemical approach highlights gabbro's low-silica, low-alkali nature, contrasting with alkalic variants that plot above the boundary and may include foid-bearing gabbros. Gabbro is distinguished from its finer-grained extrusive equivalent, basalt, primarily by texture—coarse-grained (phaneritic) due to slow cooling in plutonic settings—while sharing similar mineralogy and chemistry; intermediate rocks like diorite, however, occupy QAPF field 9 with higher silica (52-63 wt%), more sodic plagioclase (An₀-An₅₀), and increased quartz or alkali feldspar content.^[24] These boundaries ensure gabbro's placement among ultramafic to intermediate plutonics without overlapping felsic categories.

Formation

Magmatic Processes

Gabbroic magmas originate from the partial melting of mantle peridotite, primarily within the asthenosphere at depths ranging from 50 to 100 km, where melting can occur in either the spinel lherzolite stability field (shallower, approximately 50-70 km) or the garnet lherzolite field (deeper, above 70 km).^[25]^[26] This process typically involves low degrees of melting (around 5-15%) of a depleted or fertile peridotite source, producing primitive basaltic melts that are rich in magnesium and calcium, which ascend and eventually crystallize to form gabbro.^[27] The transition between spinel and garnet fields influences trace element signatures, with garnet-bearing melting retaining heavier rare earth elements in the residue.^[28] Upon reaching crustal levels, these magmas undergo fractional crystallization within magma chambers, where early-formed crystals of olivine and pyroxene settle to the chamber floor, effectively removing mafic components from the residual liquid and enriching it in plagioclase-forming constituents.^[13]^[29] This differentiation process follows Bowen's reaction series, with olivine crystallizing first at higher temperatures, followed by pyroxene, and then calcium-rich plagioclase becoming dominant in the later stages, leading to the typical mineral assemblage of gabbro.^[30] The accumulation of these cumulate layers at the base of the chamber contributes to the layered textures observed in many gabbroic intrusions. Crystallization of gabbro occurs over a temperature range of approximately 1100-1200°C, beginning with the liquidus phases and progressing as the magma cools slowly in plutonic environments.^[31]^[32] These slow cooling rates, typically on the order of 10^{-3} to 10^{-6} °C/year in deeper crustal settings, allow for the development of coarse-grained phaneritic textures characteristic of gabbro, as prolonged time enables significant crystal growth without rapid quenching.^[33]^[34] Volatiles such as H₂O and CO₂ play a crucial role in modifying mineral stability and texture during gabbro formation by lowering the solidus temperature and altering phase equilibria in the mafic magma.^[35] Increased H₂O content stabilizes hydrous phases like amphibole over pyroxene and promotes slower crystallization kinetics, leading to larger grain sizes, while CO₂ can enhance the stability of anhydrous minerals and induce textural variations such as oscillatory zoning in plagioclase through fluxing effects.^[36]^[37] These influences can result in more complex interstitial textures in volatile-enriched gabbros compared to dry systems.

Geological Settings

Gabbro primarily forms in divergent tectonic environments, particularly at mid-ocean ridges and oceanic hotspots, where it dominates the lower oceanic crust. At mid-ocean ridges, gabbro constitutes the principal lithology of seismic layer 3, which averages about 4.7 km in thickness and accounts for roughly 70% of the total oceanic crustal thickness of 6-7 km.^[38] In oceanic hotspots, gabbroic intrusions underlie thickened volcanic plateaus, forming the intrusive foundation of large oceanic crustal additions similar to those at ridges but with greater volume due to enhanced mantle melting.^[39] Within continental settings, gabbro intrudes the crust during rifting or subduction-related magmatism, often developing as layered intrusions through repeated magma injections and crystal settling. During continental rifting, mafic melts underplate or emplace as sills beneath thinning lithosphere, facilitating crustal extension.^[40] In subduction zones, gabbro arises from partial melting of the mantle wedge, intruding the overriding plate to form plutonic roots of volcanic arcs.^[41] Gabbro is a key component of ophiolite sequences, which represent obducted fragments of ancient oceanic crust and upper mantle emplaced onto continental margins during plate convergence. These complexes preserve layered gabbroic units that formed at spreading centers and were later thrust overland.^[42] In large igneous provinces (LIPs), such as those associated with flood basalts, gabbro forms voluminous intrusive layers beneath extrusive sequences, acting as the primary reservoir for magma storage and differentiation. These subvolcanic gabbroic bodies can exceed the volume of overlying lavas, stabilizing the crustal architecture of LIPs.^[43]

Varieties

Subtypes

Gabbro exhibits several subtypes distinguished primarily by variations in color, grain size, and the relative proportions of felsic (light-colored) and mafic (dark-colored) minerals, reflecting differences in their magmatic differentiation. These variants fall within the broader gabbroic rock family and are often identified through modal mineralogy, where the percentage of light minerals like plagioclase determines the classification. Leucogabbro, for instance, is a light-colored subtype characterized by a high content of plagioclase feldspar, typically exceeding 65% light minerals, often around 75-80%, with subordinate clinopyroxene and minor olivine or hornblende, resulting in a pale gray to whitish appearance.^[44] This subtype commonly forms in layered intrusions where fractional crystallization concentrates plagioclase early in the process.^[45] Mesogabbro represents an intermediate subtype, featuring a balanced composition with approximately 50-65% light minerals and 35-50% mafic minerals such as pyroxene, olivine, and amphibole, yielding a medium gray tone and coarser grain sizes in some occurrences.^[46] This variant often occurs in transitional zones of gabbroic complexes, where magma mixing or moderate differentiation produces equigranular textures without extreme enrichment in either endmember. In contrast, melagabbro is the dark-colored counterpart, dominated by more than 65% mafic minerals including abundant olivine, clinopyroxene, and iron oxides, which impart a black to deep green hue and denser structure.^[47] Melagabbro typically develops in the lower portions of intrusive bodies, where denser mafic components accumulate during crystallization.^[48] Special variants further diversify gabbro subtypes based on dominant mineral pairs. Troctolite is an olivine-plagioclase dominant subtype with pyroxene comprising less than 5% of the ferromagnesian minerals, making it a pyroxene-depleted relative of standard gabbro and often exhibiting cumulate textures in layered intrusions.^[49]^[44] Anorthositic gabbro, meanwhile, contains over 70% plagioclase with lesser amounts of mafic minerals like pyroxene or olivine, bridging the gap between pure anorthosite and typical gabbro and commonly appearing in rhythmic layering sequences.^[50]^[51] A notable ornamental variant is indigo gabbro from Madagascar, a sodalite-bearing gabbro with blue-gray hues derived from its mineral assemblage of plagioclase, sodalite, augite, and magnetite, though its petrogenetic uniqueness remains under ongoing geological investigation.^[52] This subtype's distinctive color arises from the interplay of these minerals in a brecciated texture, setting it apart from more common gabbroic rocks.

Gabbroids

Gabbroids are plutonic igneous rocks that resemble gabbro in their overall mineral assemblages, primarily featuring calcic plagioclase and mafic minerals, but differ through variations in pyroxene type, iron enrichment, or the prominence of accessory minerals such as oxides or amphiboles.^[53] These rocks are often grouped under the broader term "gabbroid" in geological classifications to encompass compositions where the plagioclase content ranges between 10% and 90% relative to pyroxene and olivine, with low quartz (<20%) or feldspathoid (<10%) presence.^[53] Unlike strict gabbro definitions, which emphasize clinopyroxene dominance, gabbroids allow for transitional or modified assemblages that blur boundaries with related mafic intrusions.^[54] A key example is norite, which shares gabbro's coarse-grained texture and plagioclase base but substitutes orthopyroxene (such as hypersthene or enstatite) for the dominant clinopyroxene found in typical gabbro, often comprising over 50% of the mafic minerals.^[54] This pyroxene shift results in a higher MgO/SiO2 ratio and less calcic character compared to gabbro. Ferrogabbro represents another variant, characterized by iron-enriched pyroxene (ferroaugite) and olivine (fayalite), where FeO content exceeds typical mafic levels, leading to darker hues and increased density.^[55] Oxide gabbro, meanwhile, incorporates abundant magnetite or ilmenite (5-15% or more), altering the rock's magnetic properties and reflecting late-stage magmatic differentiation.^[56] Distinctions among gabbroids often hinge on pyroxene ratios or accessory phases; for instance, hornblende gabbro features amphibole (hornblende) as a major mafic component exceeding 5% of femics, with pyroxene reduced below this threshold, imparting a greenish tint and potential foliation from hornblende alignment.^[44] These variations maintain the essential mafic framework—plagioclase with pyroxene or equivalents—but adapt to specific crystallization conditions without crossing into dioritic or ultramafic territories.^[57] Historically, the term "gabbroid" has served as an informal descriptor in field geology for grouping these similar rocks during mapping and reconnaissance, particularly in early 20th-century surveys of Precambrian shields where precise modal analysis was impractical.^[58] This usage facilitated broader discussions of intrusive suites without rigid taxonomy, as seen in descriptions of discontinuous gabbro-norite bodies in regions like central Wisconsin.^[58]

Distribution and Examples

Global Occurrence

Gabbro is a dominant rock type in the oceanic lithosphere, forming the bulk of the lower oceanic crust, which typically ranges from 4 to 5 km in thickness. This layer underlies the pillow basalts and sheeted dike complex of the upper crust, comprising the plutonic foundation generated at mid-ocean ridges. The oceanic crust as a whole covers approximately 60% of Earth's surface, making gabbro one of the most abundant rocks on the planet by volume, though largely hidden beneath ocean waters.^[59]^[60]^[61] In continental settings, gabbro occurs much less frequently, representing a minor component of exposed plutonic rocks—estimated at roughly 5-10%—and is commonly associated with large batholiths or as layered sills intruded into older crustal sequences. These continental occurrences reflect episodic mafic magmatism linked to rifting or subduction-related processes, but they pale in comparison to the vast oceanic reserves. The global volume of gabbro is on the order of billions of cubic kilometers, with the majority residing in the inaccessible lower oceanic crust; calculations based on an oceanic crustal area of about 300 million km² and average lower crust thickness of 4-5 km yield an estimated 1.2-1.5 billion km³.^[62]^[63]^[64] Gabbro's distribution is closely tied to major tectonic provinces, particularly divergent plate margins like the East Pacific Rise, where it crystallizes from mantle-derived melts during seafloor spreading. In convergent settings, gabbro appears in ophiolite sequences, which represent obducted fragments of ancient oceanic crust preserved in suture zones. This tectonic association underscores gabbro's role in the construction and recycling of Earth's lithosphere across plate boundaries.^[65]^[66]

Notable Localities

The Bushveld Igneous Complex in South Africa represents the world's largest layered igneous intrusion, covering approximately 66,000 km² with a volume exceeding 500,000 km³, and dated to around 2.05 Ga.^[67] It features extensive gabbroic layers within its Rustenburg Layered Suite, particularly rich in chromitite seams and platinum-group elements (PGE), making it a key site for studying magmatic differentiation and ore formation in large intrusions.^[68] The Skaergaard Intrusion in East Greenland is a classic example of a layered mafic intrusion emplaced during the Early Eocene (ca. 55–56 Ma), renowned for illustrating fractional crystallization processes in a closed-system magma chamber.^[69] Its Layered Series consists primarily of gabbroic cumulates that record progressive iron enrichment from the Lower Zone (olivine gabbro) to the Upper Zone (ferrogabbro), providing insights into cryptic and modal layering in basaltic magmas.^[70] The Rum Layered Suite, part of the Palaeocene Igneous Centre in the Inner Hebrides of Scotland (ca. 60 Ma), exposes well-preserved ultramafic and gabbroic cumulates in its Eastern, Western, and Central intrusions.^[71] These rocks display diverse cumulate textures, including adcumulates and mesocumulates, which highlight periodic influxes of primitive magma and cryptic variations in mineral compositions, serving as a model for small-scale layered intrusions.^[72] The Troodos Ophiolite in Cyprus preserves a complete section of obducted Late Cretaceous oceanic crust (ca. 92 Ma), where gabbroic rocks form the plutonic foundation underlying sheeted dikes and pillow lavas.^[73] The lower crustal gabbros, including isotropic and layered varieties, exhibit variably deformed fabrics that reflect magma chamber dynamics at a supra-subduction zone spreading center.^[74] As a modern analog to ophiolitic gabbros, the Hess Deep rift in the equatorial Pacific Ocean exposes fast-spreading lower oceanic crust through tectonic unroofing, with primitive gabbroic rocks sampled via Integrated Ocean Drilling Program (IODP) Expedition 345 in 2013.^[75] These variably depleted gabbros, including troctolites and olivine gabbros, provide direct evidence of melt extraction and crystallization processes in the plutonic section of mid-ocean ridge crust.^[76]

Uses

Construction and Ornamental

Gabbro is frequently polished and marketed as "black granite" due to its dark color and fine texture, making it suitable for dimensional stone applications such as countertops, flooring tiles, and monuments.^[77] Its durability stems from low porosity, typically ranging from 0.3% to 2.7%, which minimizes water absorption and enhances resistance to weathering.^[78] The stone's compressive strength, often exceeding 200 MPa, supports its use in load-bearing structures and high-traffic surfaces.^[79] Notable examples include the Vietnam Veterans Memorial in Washington, D.C., constructed from highly polished ultramafic gabbro quarried in Bengaluru, India, chosen for its uniform black appearance and reflective finish.^[80] Varieties such as absolute black gabbro, sourced from India and Angola, are prized for high-end ornamental finishes in luxury interiors and memorials due to their consistent deep black hue with minimal veining.^[81]^[82]

Economic and Industrial

Gabbro, particularly in layered intrusions, serves as a primary host for economically significant deposits of platinum-group elements (PGE), chromium, and vanadium. These elements are concentrated in stratiform layers within mafic-ultramafic complexes, where PGE occur in association with sulfides or chromite, chromium forms chromitite seams, and vanadium partitions into magnetite as solid solution. The Bushveld Complex in South Africa exemplifies this, hosting over half of the world's reserves of these metals in its gabbroic layers. Annual PGE production from the Bushveld reaches approximately 200 metric tons, primarily from reefs like the Merensky and UG2, underscoring its global dominance in supplying catalytic converters, electronics, and jewelry industries.^[83]^[84]^[85] Magnetitite layers within gabbro complexes also yield substantial iron ore resources, often enriched in titanium and vanadium. In such formations, dense oxide cumulates segregate during magma crystallization, forming lenses and bands exploitable for steel production and alloying. The Panzhihua intrusion in China, a gabbroic layered body, contains over 1.3 billion tons of Fe-Ti-V oxide ore in its lower zones, where titanomagnetite dominates, contributing significantly to global vanadium supply for steel strengthening.^[83]^[86] Beyond mining, gabbro finds bulk industrial applications as crushed aggregate due to its durability and angular fracture. It is extensively used in road base construction for stability under heavy loads and as railroad ballast to distribute track weight and facilitate drainage. Additionally, finely crushed gabbro serves as an abrasive in grinding and polishing operations, leveraging its hardness comparable to commercial granite.^[87]^[46] Emerging research highlights gabbro's potential in sustainable technologies, particularly carbon capture through enhanced weathering of its mafic minerals like pyroxene and olivine. These react with CO₂ to form stable carbonates, with studies screening gabbroic massifs for in situ mineralization feasibility based on fracture density and mineralogy. In oceanic settings, gabbroic crust supports geothermal energy extraction; Iceland's Deep Drilling Project, ongoing post-2020, taps superhot fluids (>500°C) from gabbroic sheeted dikes at Reykjanes, yielding high-enthalpy steam for power generation up to ten times conventional yields. Further initiatives, like the Krafla Magma Testbed, explore drilling into hot gabbroic rocks for enhanced geothermal systems by 2026–2028.^[88]^[89]^[90]

References

[1]
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### Summary of Gabbro from the PDF
[2]
What are igneous rocks? | U.S. Geological Survey - USGS.gov
Intrusive rocks have a coarse grained texture. Some common intrusive igneous rocks are granite, diorite, gabbro and peridotite. Extrusive Igneous Rocks:
[3]
Igneous Rocks - Geology (U.S. National Park Service)
Nov 8, 2023 · Igneous rocks are “fire-born,” meaning that they are formed from the cooling and solidification of molten (melted) rock.Classification of Igneous Rocks · ▻ Intrusive (Plutonic) Rock... · ▻ Gabbro · ▻ Diorite
[4]
Gabbros: Coarse-Grained Mafic Rocks
Gabbros are generally dark colored. They are dominated by Ca-rich plagioclase, which tends to be darker than the Na-rich variety, and by pyroxene.Missing: definition | Show results with:definition
[5]
Gabbro | Geology 1501 | ECU
Gabbro ; Type, Igneous Rock ; Texture, Phaneritic (Coarse-grained) ; Origin, Intrusive/Plutonic ; Chemical Composition, Mafic ; Color, Dark Gray.Missing: definition | Show results with:definition
[6]
Gabbro: Igneous Rock - Pictures, Definition & More - Geology.com
Gabbro is composed mainly of calcium-rich plagioclase feldspar (usually labradorite or bytownite) and pyroxenes (usually augite). Minor amounts of olivine might ...What Is Gabbro? · Gabbro In Oceanic Crust · Gabbro In Continental Crust
[7]
Gabbro - Geology - rocks and minerals - University of Auckland
Gabbro is a dense, mafic intrusive rock. It generally occurs as batholiths ... Colour - dark grey to black. Texture - phaneritic (medium to coarse grained).
[8]
The Density of Common Rocks and Minerals - ThoughtCo
Apr 30, 2025 · Rock Densities ; Gabbro, 2.7–3.3 ; Gneiss, 2.6–2.9 ; Granite, 2.6–2.7 ; Gypsum, 2.3–2.8.
[9]
Gabbro: The Intriguing Coarse-Grained Igneous Rock Forming ...
Hardness: 6-7 on the Mohs scale; Cleavage: None (as an aggregate rock); Fracture: Conchoidal to uneven; Luster: Submetallic to dull; Transparency: Opaque ...
[10]
Magmas and Igneous Rocks - Tulane University
Sep 3, 2015 · Chemical Composition, Temperature, Viscosity, Gas Content. Mafic or Basaltic, Basalt, Gabbro, 45-55 SiO2 %, high in Fe, Mg, Ca, low in K, Na ...<|control11|><|separator|>
[11]
ALEX STREKEISEN-Gabbro-
Gabbro is a coarse-grained rock with calcic plagioclase, pyroxene, and iron oxides, mainly clinopyroxene (augite), and named after a town in Italy.
[12]
Gabbro - Geology is the Way
Gabbro is a plutonic igneous rock and the intrusive counterpart of basalt. The name 'gabbro' derives from the Italian town of Gabbro (Rosignano Marittimo, ...Missing: etymology origin
[13]
Gabbro - Etymology, Origin & Meaning
Originating from Italian "gabbro," introduced by geologist Christian Leopold von Buch in 1809, gabbro is an igneous rock; its meaning relates to a ...
[14]
GABBRO Definition & Meaning - Merriam-Webster
more ...
[15]
Gabbro: A Coarse-Grained Mafic Intrusive Rock - Sandatlas
Feb 28, 2012 · Gabbro is a coarse-grained, dark-colored igneous rock, typically black, dark gray, or greenish, with visible crystals of light and dark ...
[16]
Cathodoluminescence images and trace element compositions of ...
Jul 1, 2017 · Gabbro in the upper part consists of 40–60 vol% plagioclase, 30–40% clinopyroxene, 10–15% Fe-Ti oxides, 5–7% fluorapatite, 2–3% amphibole, and < ...
[17]
PETROGRAPHIC, MODAL, AND MINERAL COMPOSITIONAL DATA
An average modal composition for the oxide gabbronorites is 49% plagioclase, 1% olivine, 35% clinopyroxene, 3% orthopyroxene, 11% Fe-Ti oxide, 0.5% amphibole, ...
[18]
Proc. IODP, 345, Hole U1415I
Modally, orthopyroxene-bearing olivine gabbro consists of olivine (5%–12%), plagioclase (50%–65%), clinopyroxene (20%–40%), and orthopyroxene (1%–4%), with ...
[19]
IGNEOUS PETROGRAPHY
The average modal composition of olivine gabbros is olivine = 9 vol%, plagioclase = 60 vol%, and clinopyroxene = 31 vol%. All major mineral phases show wide ...Missing: petrology | Show results with:petrology<|control11|><|separator|>
[20]
Gabbro: Mineral information, data and localities.
A gabbroid composed of 10-90% Ca-dominant plagioclase and >5% clinopyroxene. A group of basic intrusive igneous rocks composed principally of basic ...About Gabbro · Sub-divisions · Mineralogy
[21]
Geochemistry and mineral chemistry of gabbroic rocks from Horjand ...
Based on petrographic studies, the mafic igneous rocks comprise medium to coarse gabbro, micro-gabbro and hornblende-gabbro.
[22]
Ophitic texture - ALEX STREKEISEN
Ophitic texture, a variant the poikilitic texture, is one where random plagioclase laths are enclosed by pyroxene or olivine. If plagioclase is larger and ...
[23]
Estimates of the Temperature and Melting Conditions of the ...
Sep 16, 2020 · We find that the mantle has undergone less than 1% melting in the garnet-spinel transition zone—a region at about 63- to 72-km depth where these ...
[24]
[PDF] 31. mantle melting systematics: transition from continental to oceanic ...
Islands), the analysis suggested that melting was initiated at depths of. 80−100 km within the stability field of garnet lherzolite. Potential temperatures ...
[25]
Melt evolution of upper mantle peridotites and mafic dikes in the ...
Jan 5, 2018 · These dike rocks represent IAT melt products, produced by ∼7%–12% partial melting of a predominantly spinel lherzolite mantle source. The ...
[26]
Garnet in the Earth's Mantle | Elements - GeoScienceWorld
Dec 1, 2013 · Garnet does not crystallise at low pressures in most igneous systems but, in a fertile peridotite, it is stable below ~85 km depth (2.8 GPa) at ...Garnet In Upper Mantle... · Eclogites And Related Rocks... · Garnet And Geochemistry Of...<|separator|>
[27]
Crystallization Sequence and Magma Chamber Processes in the ...
Ca-rich pyroxene and plagioclase together display a well defined-magmatic lamination (Sample 9-1261.5; MCU I). (d) Gabbro (pmic-C) containing abundant. Ca-rich ...
[28]
3.3 Crystallization of Magma – Physical Geology - BC Open Textbooks
This process is known as fractional crystallization. The crystals that settle might either form an olivine-rich layer near the bottom of the magma chamber, or ...
[29]
[PDF] Gabbroic xenoliths and host ferrobasalt from the Southern Juan de ...
... crystallization temperatures of 1100”-1200'C and to host-lamellae pairs in inverted pigeonite yields subsolidus equilibrium temperatures of 1100'-1150”C.
[30]
Mobilisation of deep crustal sulfide melts as a first order control on ...
Jan 31, 2022 · This scenario occurs within a 'Goldilocks' temperature zone at ~1100–1200 ... temperature range of above 1000 °C within the cumulates after ...
[31]
Near conductive cooling rates in the upper-plutonic section of crust ...
Aug 6, 2025 · These cooling rates are greater than the minimum cooling rates of (1Á5-2Á0) Â 10 -2 C per year within the mid-to lower crust calculated by ...
[32]
Variation of cooling rate with depth in lower crust formed at an ...
Oct 16, 2001 · Cooling rates in the upper half of the gabbro section were approximately 1.5–2 times faster than in the lower half of the gabbro section during ...Missing: coarse | Show results with:coarse
[33]
Investigating the Impact of an Exsolved H2O‐CO2 Phase on Magma ...
Dec 13, 2023 · The abundance of H2O and CO2 in magmas, for example, affects the stability of mineral phases and the exsolution of a magmatic volatile phase ( ...
[34]
Experimental Constraints on Plagioclase Crystallization during H 2 ...
... water content has a noticeable effect on crystallization kinetics. Specifically, decreasing P H 2 O through the addition of CO 2 increases rates of crystal ...
[35]
Effects of CO2 flushing on crystal textures and compositions
Aug 7, 2025 · CO 2 fluxing can have widespread effects on a shallow magmatic system that vary depending on the pressure, but include the crystallization of ...
[36]
[PDF] Structure and Composition of the Mantle
Layer 3 averages 4.7 km in thickness. The complete oceanic crust is typically 6-7 km thick. There is no systematic variation in thickness of layers 2 and 3 ...
[37]
Recycled oceanic gabbro produced the depleted component in ...
May 14, 2025 · We propose these components originate from recycled high-temperature hydrothermally altered gabbroic oceanic crust, which underwent melt ...
[38]
Magmatic underplating and crustal intrusions accommodate ...
Jul 14, 2025 · This study provides the evidence of tholeiitic underplating beneath thick continental crust during early rifting, substantially postponing the onset of ...
[39]
Tectonic Setting of the Neoproterozoic Gabbroic Intrusions in ... - MDPI
The Luanchuan Neoproterozoic gabbroic intrusions are located at the southern margin of the North China Craton (NCC), intruding into the marble and schist.
[40]
Ophiolites - Volcano World - Oregon State University
Ophiolites are pieces of oceanic plate that have been thrusted (obducted) onto the edge of continental plates. · Ophiolites are characterized by a classic ...
[41]
Large Igneous Province - an overview | ScienceDirect Topics
LIPs occur both on the continents and in the oceans, and include continental flood basalts, volcanic passive margins, oceanic plateaus, submarine ridges, ...
[42]
[PDF] Resource Geology Special Issue, No. 18, 1-48, 1995
Leucocratic gabbro -- Leucogabbro is an important rock type in understanding emplacement of the ore-bearing intrusions, as first established by. LIKHACHEV (1965) ...
[43]
Geology of Corundum and Emerald Gem Deposits: A Review - GIA
Jan 31, 2020 · The geology of the Aappaluttoq deposit is dominated by an intrusive gabbro to leucogabbro sequence of rocks with significant volumes of ...
[44]
STRUCTURAL GEOLOGY - Ocean Drilling Program
Veins range from 1 mm to ~3 cm in width. Their composition ranges from leucogabbro with assemblages of plagioclase + clinopyroxene ± brown hornblende to ...
[45]
NEW DATA ON THE STRUCTURE AND AGE OF THE ALKALI ...
Nov 19, 2024 · Feldspars in mesocratic gabbro have the same characteristics as in melanocratic varieties (see Fig. 5), and leucogabbros are dominated by ...
[46]
Melagabbro: Mineral information, data and localities.
Aug 14, 2025 · Amphibole > Hornblende, AnCa2(Z2+5-mZ3+m)(Si8-(n+m)Al(n+m))(OH,F,Cl)2. Mica > Biotite, K(Fe2+/Mg)2(Al/Fe3+/Mg/Ti)([Si/Al/Fe]2Si2O10)(OH/F)2 ...
[47]
(a) Contact between olivine melagabbro (Um1) and ... - ResearchGate
The contacts between the ultramafic units are of two types: conformable and intru- sive. Along the contacts between Um1 olivine melagab- bro and Gb1 gabbro ...
[48]
ALEX STREKEISEN-Troctolite-
It is an olivine-rich, pyroxene-depleted relative of gabbro. However, unlike gabbro, no troctolite corresponds in composition to a partial melt of peridotite.
[49]
Classification of gabbros - Geology is the Way
On the other hand, both gabbro and diorite show M > 10% and plagioclase < 90%, although normally gabbros have a plagioclase content of 35 – 65% and diorites of ...
[50]
Quartz Gabbro and Anorthositic Gabbro - GeoScienceWorld
Anorthositic gabbro clasts from Cretaceous conglomerate in the Gualala area have strong resemblance to gabbroic rocks at Logan, Gold Hill, and Eagle Rest Peak ...
[51]
Formation of anorthosite-Gabbro rhythmic phase layering - USGS.gov
Rhythmically layered anorthosite and gabbro are exposed in a 4–10-m thick interval at the base of the layered gabbro unit on North Arm Mountain.Missing: definition | Show results with:definition
[52]
[PDF] APRIL 2025 - cape town gem and mineral club
Apr 5, 2025 · In Figure 21b we have a 3 cm sphere of indigo gabbro from an unrecorded site in Madagascar. This rock appears to consist of light-coloured ...
[53]
[PDF] DRAFT Geologic Map Unit Classification, ver. 6.1
Feb 8, 2002 · Gabbroid. A plutonic rock with Q < 20% or F < 10%, P/(A+P) > 65%, and pl/(pl+px+ol) between 10 and 90%. 4.5.1. Quartz monzogabbro. A plutonic ...
[54]
Norite - ALEX STREKEISEN
The principal difference between norite and gabbro, however, is the type of pyroxene of which it is composed; norite is predominately composed of ...
[55]
Definition of ferrogabbro - Mindat
Definition of ferrogabbro: A gabbro in which the pyroxene or olivine, or both, are exceptionally high in iron.
[56]
Genesis of Oceanic Oxide Gabbros and Gabbronorites During ...
Oxide gabbro shows a hypidiomorphic texture of millimetric plagioclase (50–60 vol. %), clinopyroxene (25–30 vol. %), Fe–Ti oxides (5–15 vol. %) and minor ...BATHYMETRY AND SAMPLING · PETROGRAPHY · RESULTS · DISCUSSION
[57]
Hornblende gabbro - ALEX STREKEISEN
A coarse-grained plutonic rock composed essentially of calcic plagioclase, pyroxene and iron oxides.Missing: distinctions | Show results with:distinctions
[58]
[PDF] Notes of a Geological Excursion Into Central Wisconsin
In geographical distribution the gabbros and the gabbroid rocks occupy four different and disconnected localities, viz: around Rhinelander, Merrill, Wausau ...
[59]
The Composition of the Lower Oceanic Crust in the Wadi Khafifah ...
Oct 15, 2021 · The intrusive oceanic crust is divided into lower gabbros and upper gabbros on the basis of incompatible trace element concentrations and ...
[60]
Life Found Deep inside Earth's Oceanic Crust | Scientific American
Mar 14, 2013 · This crust is several kilometers thick and covers 60% of the planet's surface, making it the largest habitat on Earth. The microbes inside it ...
[61]
Research project: The Accretion of Lower Oceanic Crust
Our current understanding of the lower oceanic crust is based on observation from ophiolites (pieces of ocean crust obducted onto continents) and geophysical ...
[62]
7 Plutons and Plutonic Rocks – Open Petrology - OpenGeology
Mafic plutonic rocks, generally simply called gabbros, or gabbroic rocks, are not as abundant as granitic rocks, but gabbroic rocks are more widespread.
[63]
The composition of the continental crust - ScienceDirect
A new calculation of the crustal composition is based on the proportions of upper crust (UC) to felsic lower crust (FLC) to mafic lower crust (MLC) of about 1: ...
[64]
Crustal thickness anomalies in the North Atlantic Ocean basin from ...
Mar 31, 2011 · Normal crust (Figure 7), here defined as crust 4–7 km thick, constitutes 58% of the total crustal area and 47% of the total crustal volume in ...<|separator|>
[65]
Upper Crustal Structure of Superfast‐Spread Oceanic Crust ...
Feb 22, 2023 · Upper oceanic crust of the superfast-spreading southern East Pacific Rise is exposed along escarpments at the Pito Deep Rift (SE Pacific) ...
[66]
Ophiolite gabbro from source to sink: A record of tectonic and ...
Aug 9, 2017 · Obduction of a large nappe composed of Jurassic and Cretaceous oceanic crust ... 2) was part of the CAO (i.e., oceanic gabbro) or part of ...
[67]
Chromitite layers indicate the existence of large, long-lived ... - NIH
The 2.05 Ga Bushveld Complex in South Africa (Fig. 1a) is the largest mafic–ultramafic layered intrusion in Earth's crust; totalling to about 600,000 km3 of ...
[68]
[PDF] Stratiform Chromite Deposit Model - USGS Publications Warehouse
the Bushveld Complex contain ~11,300 kg of PGE with about 1,100 kg added ... Bushveld Igneous Complex: Transactions of the Geological. Society of South ...
[69]
Petrology of the Skaergaard Layered Series | GEUS Bulletin
Dec 22, 2023 · The Skaergaard intrusion is a layered, ferrobasaltic intrusion emplaced during the Early Eocene into the rifting volcanic margin of East Greenland.
[70]
Differentiation and Compaction in the Skaergaard Intrusion
Since their discovery in 1930, the layered gabbro cumulates of the Skaergaard intrusion have provided insights into differentiation processes in basaltic ...Samples · Stratigraphic Systematics · Rayleigh Modelling Of P, U...
[71]
The Rum Layered Suite - ScienceDirect.com
Palaeocene igneous activity in the Rum Central Complex culminated in the formation of the ultrabasic and gabbroic rocks of the Layered Suite.
[72]
The Rum Igneous Centre, Scotland - GeoScienceWorld
Mar 3, 2017 · The easily weathered marginal gabbro of the ELI (Layered Suite) ... Classic cumulate textures in ultrabasic rocks of the Layered Suite.
[73]
The Uplift of the Troodos Massif, Cyprus - Ring - 2019 - AGU Journals
Aug 9, 2019 · It exposes a complete sequence consisting from top to bottom of marine sediments, pillow lavas, sheeted dikes, gabbros, and ultramafic rocks ...
[74]
Paleomagnetic reconstruction in the Troodos ophiolite gabbro
Nov 15, 2006 · Here we present new paleointensity results from 18 sites collected from the lower oceanic crust of the Troodos ophiolite, Cyprus (92.1 Ma old).
[75]
IODP Expedition 345: Hess Deep Plutonic Crust
Mar 4, 2013 · Integrated Ocean Drilling Program Hess Deep Expedition 345 was designed to sample lower crustal primitive gabbroic rocks that formed at the ...
[76]
Proc. IODP, 345, Expedition 345 summary - IODP Publications
Integrated Ocean Drilling Program (IODP) Hess Deep Expedition 345 was designed to sample lower crustal primitive gabbroic rock that formed at the fast ...Missing: ODP | Show results with:ODP
[77]
What Is Gabbro and How to Crush It for Construction Uses?
Sep 14, 2023 · Gabbro texture: Medium to coarse-grained; Density: 2.7-3.3 g/cm3, low porosity; Hardness: 7; Compressive strength: Greater than 280 MPa; Gabbro ...
[78]
Porosity of Rocks - Table - Matmake
Porosity of Common Rocks ; Gabbro, 0.3 - 2.7 ; Gneiss, 0.5 - 1.5 ; Granite, 0.1 - 4 ; Limestone (hard), 2.6 - 20.
[79]
Gabbro and Granite - Compare Rocks
Acid Resistant. ✓ ✘. ✓ ✘. Appearance. Veined and Shiny. Veined or Pebbled ... The commercial uses of Gabbro are cemetery markers, commemorative tablets ...
[80]
Unconfined Compression Test | Geoengineer.org
Typical Rock Types. Uniaxial Compressive Strength (MPa) ; Granite. 100-250 ; Diorite. 150-300 ; Diabase. 100-350 ; Gabbro. 150-300.
[81]
Self-Guided Tour of the Geology in D. C. Buildings - Eos.org
Dec 6, 2018 · Maya Lin's moving design is constructed from a highly polished, ultramafic gabbro. The stone was imported from Bengaluru, chosen for its ...
[82]
https://www.alibaba.com/showroom/absolute-black-granite-price.html
[83]
Absolute Black Granite Price - Premium Quality & Timely Delivery
Indian and Angolan quarries are among the most prominent suppliers, known for producing high-purity black granite with consistent grain structure and minimal ...
[84]
Platinum Group Element, Chromium, and Vanadium Deposits in ...
Jan 1, 2005 · Gabbro intrusions/massive and disseminated magnetite in gabbro ... Vanadium in layered intrusions occurs in solid solution in magnetite.
[85]
[PDF] Platinum-Group Elements in Southern Africa—Mineral Inventory and ...
This report assesses the mineral inventory and undiscovered mineral resources of platinum-group elements in Southern Africa.
[86]
PGE Production in Southern Africa, Part I - MDPI
This article provides a comprehensive summary of detailed mining data between 2010 and 2015 and discusses these in regard to the global PGE market.
[87]
Geochemistry, Petrogenesis and Metallogenesis of the Panzhihua ...
The oxide ores occur as layers and lenses within the gabbros and are concentrated in the lower parts of the intrusion. Ore textures and associated mineral ...
[88]
Gabbro - Minerals Education Coalition
The igneous rocks produced have large crystals. Gabbro has the same mineral composition as basalt (olivine and pyroxene with smaller amounts of feldspar and ...Gabbro · Type · Description<|control11|><|separator|>
[89]
Gabbro: Composition, Types, Properties, Uses - Geology In
Gabbro is a coarse-grained, dark-colored intrusive igneous rock that forms from the slow cooling and crystallization of mafic magma beneath the Earth's surface.Gabbro Composition · How Is Gabbro Formed · Gabbro Uses
[90]
Mineral Carbonation of CO2 in Mafic Plutonic Rocks, I—Screening ...
Jul 16, 2020 · This article describes the screening, ranking and characterization of ultramafic and mafic rocks in southern Portugal for mineral carbonation
[91]
Geothermal energy and ore-forming potential of 600 °C mid-ocean ...
Aug 19, 2020 · INTRODUCTION AND GEOLOGICAL BACKGROUND. The Iceland Deep Drilling Project (IDDP) explores the economic potential of geothermal fluids in the ...
[92]
Magma and hot rocks: Iceland seeks the future of geothermal energy
Jul 22, 2024 · Iceland is at the fore, with new research that aims to harness heat from volcanoes and superhot formations.Missing: gabbro 2020