Types of Rocks


Igneous

A sample of andesite (dark groundmass) with amygdaloidal vesicules filled with zeolite. Diameter of view is 8 cm.

Andesite – an Intermediate volcanic rock
Anorthosite – an igneous ultramafic rock composed predominantly of plagioclase
Aplite – a very fine grained intrusive igneous rock
Basalt – a volcanic rockof mafic composition

Adakite – a class of basaltic rocks containing low yttrium and ytterbium
Hawaiite – a class of basalts formed from ocean island (hot spot) magmatism
Basanite – a volcanic rock of mafic composition; essentially a silica undersaturated basalt
Boninite – a high-magnesian basalt dominated by pyroxene
Carbonatite – a rare igneous rock composed of >50% carbonate minerals
Charnockite – a type of granite containing pyroxene

Enderbite – a variety of charnockite
Dacite – a felsic to intermediate volcanic rock with high iron content
Diabase or dolerite – an intrusive mafic rock forming dykes or sills
Diorite – a coarse grained intermediate plutonic rock composed of plagioclase, pyroxene and/or amphibole
Dunite – an ultramafic cumulate rock composed of olivine and accessories
Essexite – a silica undersaturated mafic plutonic rock (essentially a foid-bearing gabbro)
Foidolite – a plutonic igneous rock composed of >90% feldspathoid minerals
Gabbro – a coarse grained plutonic rock composed of pyroxene and plagioclase basically equivalent to basalt
Granite – a coarse grained plutonic rock composed of orthoclase, plagioclase and quartz
Granodiorite – a granitic plutonic rock with plagioclase > orthoclase
Granophyre – a subvolcanic intrusive rock of granitic composition
Harzburgite – a variety of peridotite; an ultramafic cumulate rock
Hornblendite – a mafic or ultramafic cumulate rock dominated by >90% hornblende
Hyaloclastite – a volcanic rock composed primarily of glasses and glassy tuff
Icelandite – a volcanic rock
Ignimbrite – a fragmental volcanic rock
Ijolite – a very rare silica-undersaturated plutonic rock

Limey shale overlaid by limestone. Cumberland Plateau, Tennessee
Kimberlite – a rare ultramafic, ultrapotassic volcanic rock and a source of diamonds
Komatiite – an ancient ultramafic volcanic rock
Lamproite – an ultrapotassic volcanic rock
Lamprophyre – an ultramafic, ultrapotassic intrusive rock dominated by mafic phenocrysts in a feldspar groundmass
Latite – a silica undersaturated form of andesite
Lherzolite – an ultramafic rock, essentially a peridotite
Monzogranite – a silica undersaturated granite with <5% normative quartz
Monzonite – a plutonic rock with <5% normative quartz
Nepheline syenite – a silica undersaturated plutonic rock with nepheline replacing orthoclase
Nephelinite – a silica undersaturated plutonic rock with >90% nepheline
Norite – a hypersthene bearing gabbro
Obsidian – a type of volcanic glass
Pegmatite – an igneous rock (or metamorphic rock) with giant sized crystals
Peridotite – a plutonic or cumulate ultramafic rock composed of olivine and pyroxene
Phonolite – a silica undersaturated volcanic rock; essentially similar to nepheline syenite
Picrite – an olivine-bearing basalt

Quartzite

Porphyry – a rock, usually granitic, with a porphyritic texture
Pumice – a fine grained, extremely vesicular volcanic rock
Pyroxenite – a coarse grained plutonic rock composed of >90% pyroxene
Quartz diorite – a diorite with >5% modal quartz
Quartz monzonite – an intermediate plutonic rock, essentially a monzonite with 5-10% modal quartz
Rhyodacite – a felsic volcanic rock which is intermediate between a rhyolite and a dacite
Rhyolite- a felsic volcanic rock

Comendite – a peralkaline rhyolite
Pantellerite – an alkaline rhyolite-rhyodacite with amphibole phenocrysts
Scoria – an extremely vesicular mafic volcanic rock
Sovite – a coarse grained carbonatite rock
Syenite – a plutonic rock dominated by orthoclase feldspar; a type of granitoid
Tachylyte – essentially a basaltic glass
Tephrite – a silica undersaturated volcanic rock; can be a generic term
Tonalite – a plagioclase-dominant granitoid
Trachyandesite- an alkaline intermediate volcanic rock

Benmoreite – sodic trachyandesite
Basaltic trachyandesite

Mugearite – sodic basaltic trachyandesite
Shoshonite – potassic basaltic trachyandesite
Trachyte – a silica undersaturated volcanic rock; essentially a feldspathoid-bearing rhyolite
Troctolite – a plutonic ultramafic rock containing olivine, pyroxene and plagioclase
Trondhjemite – a form of tonalite where plagioclase-group feldspar is oligoclase
Tuff – a fine grained volcanic rock formed from volcanic ash
Websterite – a type of pyroxenite, composed of clinoproxene and orthopyroxene
Wehrlite – an ultramafic plutonic or cumulate rock, a type of peridotite, composed of olivine and clinopyroxene

Sedimentary

Bituminous coal seam in West Virginia

Dolomite crystals from Touissite, Morocco

Turbidite (Gorgoglione Flysch), Miocene, South Italy

Argillite – a sedimentary rock composed primarily of clay-sized particles
Arkose – a sedimentary rock similar to sandstone
Banded iron formation – a fine grained chemical sedimentary rock composed of iron oxide minerals
Breccia – a sedimentary or tectonic rock composed of fragments of other, broken rocks
Chalk – a sedimentary rock composed primarily of coccolith fossils
Chert – a fine grained chemical sedimentary rock composed of silica
Claystone – a sedimentary rock formed from clay
Coal – a sedimentary rock formed from organic matter
Conglomerate- a sedimentary rock composed of large rounded fragments of other rocks

Diamictite – a poorly sorted conglomerate
Coquina – a sedimentary carbonate rock formed by accumulation of abundant shell fossils and fragments
Diatomite – a sedimentary rock formed from diatom fossils
Dolomite or dolostone – a carbonate rock composed of the mineral dolomite +/- calcite
Evaporite – a chemical sedimentary rock formed by accumulation of minerals after evaporation
Flint – a form of chert
Greywacke – an immature sandstone with quartz, feldspar and rock fragments within a clay matrix
Gritstone – essentially a coarse sandstone formed from small pebbles
Itacolumite – porous, yellow sandstone
Jaspillite – an iron-rich chemical sedimentary rock similar to chert or banded iron formation
Laterite – a residual sedimentary rock formed from a parent rock under tropical conditions
Lignite – a sedimentary rock composed of organic material; otherwise known as Brown Coal
Limestone – a sedimentary rock composed primarily of carbonate minerals
Marl – a limestone with a considerable proportion of silicate material
Mudstone – a sedimentary rock composed of clay and muds
Oil shale – a sedimentary rock composed dominantly of organic material
Oolite – a chemical sedimentary limestone
Sandstone – a clastic sedimentary rock defined by its grain size
Shale – a clastic sedimentary rock defined by its grain size
Siltstone – a clastic sedimentary rock defined by its grain size
Travertine – a sedimentary rock containing calcite and iron oxides
Turbidite – a particular sequence of sedimentary rocks which form within the deep ocean environment
Wackestone – a matrix-supported carbonate sedimentary rock.

Metamorphic

Phyllite

Banded gneiss with a dike of granite orthogneiss

Marble

Manhattan Schist, from Southeastern New York

Slate

Anthracite – a type of coal
Amphibolite – a metamorphic rock composed primarily of amphibole
Blueschist – a metamorphic rock composed of sodic amphiboles with a distinct blue color
Cataclasite – a rock formed by faulting
Eclogite – an ultra-high grade metamorphosed basalt or gabbro; also a facies of metamorphic rocks
Gneiss – a coarse grained metamorphic rock
Gossan – the product of the weathering of a sulfide rock or ore body
Granulite – a high grade metamorphic rock formed from basalt; also a facies of metamorphic rocks
Greenschist- a generic term for a mafic metamorphic rock dominated by green amphiboles

Greenstone
Hornfels – a metamorphic rock formed by heating by an igneous rock
Marble – a metamorphosed limestone
Migmatite – a high grade metamorphic rock verging upon melting into a magma
Mylonite – a metamorphic rock formed by shearing
Metapelite – a metamorphic rock with a protolith of clay-rich (siltstone) sedimentary rock
Phyllite – a low grade metamorphic rock composed mostly of micaceous minerals
Metapsammite – a metamorphic rock with a protolith of quartz-rich (sandstone) sedimentary rock
Pseudotachylite – a glass formed by melting within a fault via friction
Quartzite – a metamorphosed sandstone typically composed of >95% quartz
Schist – a low to medium grade metamorphic rock
Serpentinite – a metamorphosed ultramafic rock dominated by serpentine minerals
Skarn – a metasomatic rock
Slate – a low grade metamorphic rock formed from shale or silts
Suevite – a rock formed by partial melting during a meteorite impact
Talc carbonate – a metamorphosed ultramafic rock with talc as an essential constituent; similar to a serpentinite

Soapstone – essentially a talc schist
Whiteschist – a high pressure metamorphic rock containing talc + kyanite

Specific varieties of rocks

The following terms are used to describe rocks which are not petrographically or genetically distinct, but are defined according to various other criteria; most are specific classes of other rocks, or altered versions of existing rocks. Some archaic and vernacular terms for rocks are also included.

Adamellite – a variety of quartz monzonite
Appinite – a group of varieties of lamprophyre, mostly rich in hornblende
Aphanite – an aphanitic felsic volcanic rock which confounds identification via optical means
Borolanite – a variety of nepheline syenite from Loch Borralan, Scotland
Blue Granite – essentially larvikite, a monzonite
Epidosite – a type of metasomatite; essentially altered basalt
Felsite – an aphanitic felsic volcanic rock which confounds identification via optical means
Flint – typically a form of chert, jasper, or tuff
Ganister – a Cornish term for a palaeosol formed on sandstone
Ijolite – a silica-undersaturated plutonic rock associated with nepheline syenites
Jadeitite – a very rare rock formed by concentration of jadeite pyroxene; a form of serpentinite
Jasperoid – a hematite-silica metasomatite analogous to a skarn
Kenyte – a variety of phonolite, first found on Mount Kenya
Vogesite – a variety of lamprophyre
Larvikite – a variety of monzonite with microperthitic ternary feldspars from Larvik, Norway
Litchfieldite – a metamorphosed nepheline syenite occurrence near Litchfield, Maine
Luxullianite – a tourmaline-bearing granite with a peculiar texture, occurring at Luxulyan, Cornwall, England
Mangerite – a hypersthene-bearing monzonite
Minette – a variety of lamprophyre
Novaculite – a chert formation found in Oklahoma, Arkansas and Texas
Pyrolite – a chemical analogue considered to theoretically represent the earth’s upper mantle
Rapakivi granite – a granite which exhibits the peculiar rapakivi texture
Rhomb porphyry – a type of latite with euhedral rhombic phenocrysts of feldspar
Shonkinite – an archaic and informal term used to describe melitilic and kalsititic rocks; often used today
Taconite – a term for banded iron formation primarily used in the United States of America
Teschenite – essentially a silica undersaturated, analcime bearing gabbro
Theralite – essentially a nepheline gabbro
Variolite – devitrified glass
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Posted on July 11, 2012, in Categorized. Bookmark the permalink. 1 Comment.

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