Types of Rocks

The following is a list of rock types recognized by geologists.

Any unique combination of chemical composition, mineralogy, grain size, texture, or other distinguishing characteristics can describe a rock type. Additionally, different classification systems exist for each major type of rock. There is no agreed number of specific types of rocks.

There are three major types of rock:

igneous rock
metamorphic rock
sedimentary rock

We are working on adding articles to the types of rocks found in the Southwest.

Igneous Rocks

Adakite – Volcanic rock type
Andesite – Type of volcanic rock
Alkali feldspar granite – Type of igneous rock rich in alkali feldspar
Anorthosite – Mafic intrusive igneous rock composed predominantly of plagioclase
Aplite – Fine-grained intrusive igneous rock type similar to granite
Basalt – Magnesium- and iron-rich extrusive igneous rock
ʻAʻā – Basaltic lava with a crumpled appearance
Pāhoehoe – Basaltic lava with a flowing, often ropy appearance
Basaltic trachyandesite
Mugearite – Volcanic rock type
Shoshonite – Potassium-rich variety of basaltic trachyandesite
Basanite – A silica-undersaturated basalt
Blairmorite – Rare porphyritic volcanic rock
Boninite – Ultramafic extrusive rock high in both magnesium and silica
Carbonatite – Igneous rock with more than 50% carbonate minerals
Charnockite – Type of granite containing orthopyroxene
Enderbite – Igneous rock of the charnockite series
Dacite – Volcanic rock intermediate in composition between andesite and rhyolite
Diabase, also known as dolerite – Type of igneous rock
Diorite – Igneous rock type
Napoleonite, also known as corsite – Variety of diorite with orbicular structure
Dunite – Ultramafic and ultrabasic rock from Earth’s mantle which is made of the mineral olivine
Essexite – Dark gray or black holocrystalline plutonic rock
Foidolite – Igneous rock rich in feldspathoid minerals
Gabbro – Coarse-grained mafic intrusive rock
Granite – Common type of intrusive, felsic, igneous rock with granular structure
Granodiorite – Type of coarse grained intrusive igneous rock
Granophyre – Subvolcanic rock that contains quartz and alkali feldspar in characteristic angular intergrowths
Harzburgite – Ultramafic mantle rock
Hornblendite – Plutonic rock consisting mainly of the amphibole hornblende
Hyaloclastite – Volcaniclastic accumulation or breccia
Icelandite – Iron rich, aluminium poor andesite
Ignimbrite – Variety of hardened tuff
Ijolite – Igneous rock consisting essentially of nepheline and augite
Kimberlite – Igneous rock which sometimes contains diamonds
Komatiite – Ultramafic mantle-derived volcanic rock
Lamproite – Ultrapotassic mantle-derived volcanic or subvolcanic rock
Lamprophyre – Ultrapotassic igneous rocks – An ultramafic, ultrapotassic intrusive rock dominated by mafic phenocrysts in a feldspar groundmass
Latite – Type of volcanic rock – A silica-undersaturated form of andesite
Lherzolite – An ultramafic rock, essentially a peridotite
Monzogranite – A silica-undersaturated granite with <5% normative quartz
Monzonite – Igneous intrusive rock with low quartz and equal plagioclase and alkali feldspar – a plutonic rock with <5% normative quartz Nepheline syenite – A silica-undersaturated plutonic rock of nepheline and alkali feldspar Nephelinite – Igneous rock made up almost entirely of nepheline and clinopyroxene – A silica-undersaturated plutonic rock with >90% nepheline
Norite – A hypersthene-bearing gabbro
Obsidian – Naturally occurring volcanic glass
Pegmatite – Igneous rock with very large interlocked crystals
Peridotite – Coarse-grained ultramafic igneous rock type
Phonolite – Uncommon extrusive rock – A silica-undersaturated volcanic rock; essentially similar to nepheline syenite
Phonotephrite – A volcanic rock with a composition between phonolite and tephrite
Picrite – An olivine-bearing basalt
Porphyry – Textural form of igneous rock with large grained crystals in a fine matrix
Pumice – Light colored highly vesicular volcanic rock
Pyroxenite – Igneous rock – a coarse grained plutonic rock composed of >90% pyroxene
Quartz diorite – Igneous, plutonic rock – A diorite with >5% modal quartz
Quartz monzonite – Type of igneous rock – An intermediate plutonic rock, essentially a monzonite with 5–10% modal quartz
Quartzolite – Extremely rare igneous rock made mostly of quartz – An intrusive rock composed mostly of quartz
Rhyodacite – Volcanic rock rich in silica and low in alkali metal oxides – A felsic volcanic rock which is intermediate between a rhyolite and a dacite
Rhyolite – Igneous, volcanic rock, of felsic (silica-rich) composition
Comendite – Hard, peralkaline igneous rock, a type of light blue grey rhyolite
Pantellerite – Peralkaline rhyolite type of volcanic rock
Scoria – Dark vesicular volcanic rock
Shonkinite – Intrusive igneous rock – a plutonic rock
Sovite – A coarse-grained carbonatite rock
Syenite – Intrusive igneous rock – A plutonic rock dominated by orthoclase feldspar; a type of granitoid
Tachylyte – Essentially a basaltic glass
Tephriphonolite – A volcanic rock with a composition between phonotephrite and phonolite
Tephrite – Igneous, volcanic rock – A silica-undersaturated volcanic rock
Tonalite – A plagioclase-dominant granitoid
Trachyandesite – An alkaline intermediate volcanic rock
Benmoreite – Silica-undersaturated volcanic rock of intermediate composition – sodic trachyandesite
Trachybasalt – A volcanic rock with a composition between basalt and trachyte
Hawaiite – Volcanic rock – a sodic type of trachybasalt, typically formed by ocean island (hot spot) volcanism
Trachyte – Extrusive igneous rock – A silica-undersaturated volcanic rock; essentially a feldspathoid-bearing rhyolite
Troctolite – Igneous rock – A plutonic ultramafic rock containing olivine, pyroxene and plagioclase
Trondhjemite – Light-colored intrusive igneous rock – A form of tonalite where plagioclase-group feldspar is oligoclase
Tuff – Rock consolidated from volcanic ash
Websterite – A type of pyroxenite, composed of clinoproxene and orthopyroxene
Wehrlite – Ultramafic rock – An ultramafic plutonic or cumulate rock, a type of peridotite, composed of olivine and clinopyroxene

Sedimentary Rocks

Turbidite (Gorgoglione Flysch), Miocene, South Italy
Argillite – Sedimentary rock, mostly of indurated clay particles
Arkose – Type of sandstone containing at least 25% feldspar
Banded iron formation – Distinctive layered units of iron-rich sedimentary rock that are almost always of Precambrian age
Breccia – Rock composed of broken fragments cemented by a matrix
Calcarenite – Type of limestone that is composed predominantly of sand-size grains
Chalk – Soft, white, porous sedimentary rock made of calcium carbonate
Chert – Hard, fine-grained sedimentary rock composed of cryptocrystalline silica
Claystone – Clastic sedimentary rock composed primarily of clay-sized particles
Coal – Combustible sedimentary rock composed primarily of carbon
Conglomerate – Coarse-grained clastic sedimentary rock with mainly rounded to subangular clasts
Coquina – Sedimentary rock that is composed mostly of fragments of shells
Diamictite – Type of sedimentary rock
Diatomite – Soft, siliceous sedimentary rock that is easily crumbled
Dolomite (rock), also known as Dolostone – Sedimentary carbonate rock that contains a high percentage of the mineral dolomite
Evaporite – Water-soluble mineral deposit formed by evaporation from an aqueous solution
Flint – Cryptocrystalline form of the mineral quartz
Geyserite – Form of opaline silica that is often found around hot springs and geysers
Greywacke – Hard, dark sandstone with poorly sorted angular grains in a compact, clay-fine matrix
Gritstone – Hard, coarse-grained, siliceous sandstone
Itacolumite – A porous, yellow sandstone or schistose quartzite that is flexible when cut into thin strips
Jaspillite – Banded mixture of hematite and quartz
Laterite – Product of rock weathering in wet tropical climate rich in iron and aluminum
Lignite – Soft, brown, combustible, sedimentary rock
Limestone – Sedimentary rocks made of calcium carbonate
Marl – Lime-rich mud or mudstone which contains variable amounts of clays and silt
Mudstone – Fine grained sedimentary rock whose original constituents were clays or muds
Oil shale – Organic-rich fine-grained sedimentary rock containing kerogen
Oolite – Sedimentary rock formed from ooids
Phosphorite – Sedimentary rock containing large amounts of phosphate minerals – A non-detrital sedimentary rock that contains high amounts of phosphate minerals
Sandstone – Type of sedimentary rock
Shale – Fine-grained, clastic sedimentary rock
Siltstone – Sedimentary rock which has a grain size in the silt range
Sylvinite – A sedimentary rock made of a mechanical mixture of sylvite and halite
Tillite – Till which has been indurated or lithified by burial
Travertine – Form of limestone deposited by mineral springs
Tufa – Porous limestone rock formed when carbonate minerals precipitate out of ambient temperature water
Turbidite – Geologic deposit of a turbidity current
Wackestone – Mud-supported carbonate rock that contains greater than 10% grains

Metamorphic Rocks

Anthracite – Hard, compact variety of coal
Amphibolite – A metamorphic rock containing mainly amphibole and plagioclase
Blueschist – Metavolcanic rock that forms by the metamorphism of basalt and rocks with similar composition
Cataclasite – A rock formed by faulting
Eclogite – A dense metamorphic rock formed under high pressure
Gneiss – Common high-grade metamorphic rock
Granulite – Class of high-grade medium to coarse grained metamorphic rocks
Greenschist – Metamorphic rocks – A mafic metamorphic rock dominated by green amphiboles
Hornfels – Calcflinta – A type of hornfels found in the Scottish Highlands
Litchfieldite – Nepheline syenite gneiss
Marble – Non-foliated, metamorphic rock, commonly used for sculpture and as a building material – a metamorphosed limestone
Migmatite – Mixture of metamorphic rock and igneous rock
Mylonite – Metamorphic rock – A metamorphic rock formed by shearing
Metapelite – A metamorphic rock with a protolith of clay-rich (siltstone) sedimentary rock
Metapsammite – A metamorphic rock with a protolith of quartz-rich (sandstone) sedimentary rock
Phyllite – Type of foliated metamorphic rock – A low grade metamorphic rock composed mostly of micaceous minerals
Pseudotachylite – A glass formed by melting within a fault via friction
Quartzite – Hard, non-foliated metamorphic rock which was originally pure quartz sandstone – A metamorphosed sandstone typically composed of >95% quartz
Schist – Easily split medium-grained metamorphic rock
Serpentinite – Rock formed by hydration and metamorphic transformation of olivine
Skarn – Hard, coarse-grained, hydrothermally altered metamorphic rocks
Slate – Metamorphic rock – A low grade metamorphic rock formed from shale or silts
Suevite – Rock consisting partly of melted material formed during an impact event – 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 – Talc-bearing metamorphic rock – Essentially a talc schist
Tectonite – A rock whose fabric reflects the history of its deformation
Whiteschist – A high pressure metamorphic rock containing talc and kyanite

Specific Varieties

The following are terms for rocks that 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 – Igneous rock composed of very small crystals invisible to the naked eye
Borolanite – Variety of nepheline syenite from Loch Borralan, Scotland – A variety of nepheline syenite from Loch Borralan, Scotland
Blue Granite – Variety of monzonite, an igneous rock
Epidosite – Hydrothermally altered epidote- and quartz-bearing rock
Felsite – Very fine grained felsic volcanic rock that may or may not contain larger crystals
Flint – Cryptocrystalline form of the mineral quartz
Ganister – Hard, fine-grained quartzose sandstone, or orthoquartzite
Gossan – Intensely oxidized, weathered or decomposed rock
Hyaloclastite – Volcaniclastic accumulation or breccia
Ijolite – Igneous rock consisting essentially of nepheline and augite
Jadeitite – Metamorphic rock found in blueschist-grade metamorphic terranes
Jasperoid – A hematite-silica metasomatite analogous to a skarn
Kenyte – Type of igneous rock – A variety of phonolite, first found on Mount Kenya
Lapis lazuli – Contact metamorphic rock containing lazurite, pyrite and calcite – A rock composed of lazurite and other minerals
Larvikite – Variety of monzonite, an igneous rock
Litchfieldite – A metamorphosed nepheline syenite occurrence near Litchfield, Maine
Llanite – A hypabyssal rhyolite with microcline and blue quartz phenocrysts from the Llano Uplift in Texas
Luxullianite – Rare type of granite
Mangerite – Plutonic intrusive igneous rock, that is essentially a hypersthene-bearing monzonite
Minette – A variety of lamprophyre
Novaculite – A type of chert found in Oklahoma, Arkansas, and Texas
Pietersite – Breccia rock of hawk’s eyes and tiger’s eyes
Pyrolite – A chemical analogue considered to theoretically represent the earth’s upper mantle
Rapakivi granite – Type of igneous rock
Rhomb porphyry – A type of latite with euhedral rhombic phenocrysts of feldspar
Rodingite – A mafic rock metasomatized by serpentinization fluids
Shonkinite – Intrusive igneous rock – melitilic and kalsititic rocks
Taconite – Variety of iron-bearing sedimentary rock
Tachylite – Form of basaltic volcanic glass
Teschenite – A silica undersaturated, analcime bearing gabbro
Theralite – A nepheline gabbro
Unakite – An altered granite
Variolite – Igneous rocks which contain varioles
Vogesite – Ultrapotassic igneous rocks – A variety of lamprophyre
Wad – A rock rich in manganese oxide or manganese hydroxide

Resources Used

Wikipedia – Rock Types