Gossan is an iron and manganese-bearing weathered product overlying a sulphide deposit. Most ore deposits contain the iron sulphide pyrite, which reacts with water and oxygen at the surface to form two important products. One is insoluble iron oxides, which are deposited at the surface where they form, making a layer of distinctively red to orange coloured rock which is gossan. The second product is an iron sulphate which is soluble and strongly oxidising, and trickles down through the deposit.

Lignite

Lignite, or brown coal, is a soft, brown, combustible, sedimentary rock formed from naturally compressed peat.

Greenstone

Greenstone is any compact dark-green altered or metamorphosed basic igneous rock that owes its colour to the presence of chlorite, actinolite or epidote.

Breccia

Breccia is a sedimentary or igneous rock made up of angular fragments.

Suevite

Suevite is an impact breccia that contains shocked and unshocked clasts in a clastic matrix along with cogenetic melt particles. It is one of the diagnostic rock-types for large impact structures. It has been described from many of the larger impact structures identified on earth (Mindat).

PLUTONIC IGNEOUS ROCKS

Quartzolite

Quartzolite is a plutonic igneous rock that contains 90 - 100% quartz and 0 - 10% feldspar.
The essential constituent is quartz.
Common but not essential constituents include K-feldspars and plagioclase feldspars.

Granite

Granite is a medium- to coarse-grained silica-rich plutonic igneous rock, formed by crystallisation of a silica-rich magma in a major intrusion. It contains
80 - 100 % light coloured minerals, of which quartz is 20 - 60% and feldspars 40 - 80%. Of these feldspars 35 - 100% are K-feldspars and 0 - 65% plagioclase feldspars.
It also contains 0 - 20% dark minerals.
Essential constituents are quartz and K-feldspars (feldspars rich in potassium).
Common but not essential constituents include biotite, hornblende, muscovite and plagioclase feldspars (feldspars deficient in potassium).

Granitoid

Granitoid is a coarse grained igneous rock composed mostly of quartz and K-feldspar, with 20% to 60% quartz. It usually contains minor micas and/or amphiboles (Mindat).

Leucogranite

Leucogranite is a granite having more light coloured minerals than dark ones.

Metagranite

Metagranite is a metamorphosed granite.

Monzogranite

Monzogranite is a granite having a K-feldspar/total feldspars ratio from 0.35-0.65 (Mindat).

Alaskite

Alaskite is a light coloured K-feldspar granite consisting almost entirely of quartz and K-feldspar

Ekerite

Ekerite is a K-feldspar granite containing anorthoclase and microperthite with small amounts of arfvedsonite and aegirine (Mindat).

Granodiorite

Granodiorite is a feldspar-rich plutonic igneous rock.
Major constituents are plagioclase feldspar, K-feldspar, quartz and mica.
Minor constituents are hornblende and augite. Oligoclase is a common constituent.
Granodiorite is the most abundant of the plutonic igneous rocks.

Tonalite

Tonalite is a plutonic igneous rock.
Major constituents are plagioclase feldspar, typically oligoclase or albite variety andesine (greater than 10%), and quartz (greater than 20%), hornblende and biotite.
Minor constituents are K-feldspars (10% or less), apatite, titanite, magnetite, ilmenite and zircon.

Syenite

Syenite is a coarse-grained plutonic igneous rock with intermediate silica content. It contains
60 - 100 % light coloured minerals of which feldspar is 80 - 100% and quartz 0 - 20% or feldspathoids 0 - 10%.
Of the feldspars, 65 - 100% are K-feldspars and 0 - 35% plagioclase feldspar feldspar (albite to anorthite).
It also contains 0 - 40% dark minerals.
The essential constituents are K-feldspars.
Common but not essential constituents include aenigmatite, amphibole, biotite, feldspathoids, hornblende, plagioclase feldspar, pyroxene, titanite and zircon (very common in nepheline syenite).

Albitite

Albitite is a variety of alkali feldspar syenite consisting almost entirely of albite, usually a high to medium-temperature metasomatic rock formed by the intense sodic alteration of various rocks.

Shonkinite

Shonkinite is a dark-colored syenite composed chiefly of augite and K-feldspar, and possibly containing olivine, hornblende , biotite and nepheline (Mindat).

Nepheline Syenite

Nepheline syenite is a nepheline-rich syenite.
The essential constituents are K-feldspars and nepheline.
Common but not essential constituents include biotite and hornblende.
Foyaite is a nepheline syenite with predominant orthoclase and a trachytic texture

Lujavrite

Lujavrite is a melanocratic agpaitic variety of nepheline syenite rich in eudialyte, arfvedsonite and aegirine with perthitic alkali feldspar or separate microcline and albite. A pronounced igneous lamination is characteristic (Mindat).

Foyaite

Foyaite is a hypersolvus nepheline syenite sometimes used as a group name for nepheline syenites. Now used as a term for nepheline syenites having a trachytic texture caused by the platy K-feldspar crystals. A nepheline syenite with predominant orthoclase and a trachytic texture (Mindat).

Naujaite

Naujaite is a nepheline-sodalite syenite comprising crystals of feldspathoid minerals enclosed in alkali feldspar and ferromagnesian silicates (Strekeisen).

Agpaite

Agpaite is a K-feldspar nepheline syenite characterised by complex zirconium and titanium minerals such as eudialyte rather than simple minerals such as zircon or ilmenite (Mindat).

Ijolite

Ijolite is a series of plutonic igneous rocks containing nepheline and 30% to 60% mafic minerals, generally clinopyroxene, and including minor titanite, apatite and andradite variety melanite (Mindat).

Monzonite

Monzonite is a plutonic igneous rock containing 0 to 5% quartz and 95 to 100% feldspar.
Essential constituents are K-feldspars and plagioclase feldspars.
Common but not essential minerals include amphibole and pyroxene.
Disseminated copper deposits are found frequently in monzonite.

Diorite

Diorite is a plutonic igneous rock with intermediate silica content. It contains
50 - 85% of light coloured minerals of which feldspars are 80 - 100% and quartz is 0 - 20% or feldspathoids 0 - 10%.
Of the feldspars, 65 - 100% are plagioclase feldspars and 0 - 35% are K-feldspars.
It also contains 15 - 50% dark minerals.
The essential constituent is plagioclase feldspar.
Common but not essential constituents include biotite, hornblende and quartz.

Dolerite

Dolerite is a medium grained mafic plutonic igneous rock whose main components are calcium-bearing plagioclase and clinopyroxene.
Metadolerite is a metamorphosed dolerite.

Gabbro

Gabbro is a silica-poor plutonic igneous rock. It contains
35 - 80% of light coloured minerals of which feldspars are 80 - 100% and quartz is 0 - 20% or feldspathoids 0 - 10%.
Of the feldspars, 65 - 100% are plagioclase feldspar feldspars and 0 - 35% are K-feldspars.
It also contains 20 - 65% dark minerals.
Essential constituents are plagioclase feldspars and dark minerals (mafic minerals) such as olivine and pyroxene.
Common but not essential constituents include biotite and hornblende.
Gabbro is most abundant at constructive plate margins, where tectonic plates move apart and magma wells up to fill the gap, and gabbro constitutes the lower portions of the oceanic crusts. It is also abundant in oceanic islands; these are islands without any foundation of continental rock, usually formed as the result of volcanic action.
Gabbro can also occur at destructive plate margins, where the tectonic plates are moving together, and in continental rifts, where the continental crust is thinning due to the underlying plates moving apart.
Nickel ores are associated with norites and peridotite (P&M).

Metagabbro

Metagabbro is a metamorphically-altered gabbro.

Gabbronorite

Gabbronorite is a gabbroid with <5% olivine and subequal amounts of clino- and ortho- pyroxenes (Mindat).

teschenite

Teschenite is a variety of analcime-gabbro consisting of olivine, titanium-bearing augite, labradorite and analcime (Mindat).

Essexite

Essexite is a variety of alkali gabbro primarily composed of plagioclase, hornblende, biotite and titanium-bearing augite, with lesser amounts of K-feldspar and nepheline (Mindat).

Troctolite

Troctolite is a gabbro with <5% pyroxene and is composed chiefly of calcic plagioclase, such as labradorite, and olivine. Such rocks commonly are speckled like trout (Mindat).

Larvikite

Larvikite is an intermediate plutonic igneous rock. Essential constituents are feldspar, pyroxene (usually augite), mica and amphibole . Common but not essential constituents are nepheline, olivine and quartz (Pellant, Mindat).

Anorthosite

Anorthosite is a mafic plutonic igneous rock, formed by crystallisation of a silica-poor magma in a major intrusion. It contains at least 90% calcium-rich plagioclase feldspar. The remaining 10% is made up of olivine, garnet, pyroxene and iron oxides.
The essential constituent is plagioclase feldspar.
Common but not essential constituents include pyroxene.

Foidolite

Foidolite is a coarse-grained plutonic igneous rock containing less than 90% mafics and more than 10% felsics, of which more than 60% are feldspathoids (Mindat).

Nephelinolite

Nephelinolite is a foidolite where nepheline is the most abundant feldspathoid (Mindat).

Melanocratic nephelinolite

Melanocratic nephelinolite is a nephelinolite consisting of 10% to 30% nepheline with pyroxene. Previously called melteigite (Mindat).

Aplite

Aplite is a fine-grained granite consisting of only feldspar and quartz.
Essential constituents are K-feldspar, plagioclase feldspar and quartz.

Mafic and Ultramafic

Mafic rocks are rocks that are rich in dark minerals such as magnesium and iron compounds but deficient in quartz. Common rock-forming mafic minerals include olivine, pyroxene, and biotite.
Ultramafic rocks contain more than 90% mafic minerals. Ultrabasic rocks are igneous rocks with a silica content below 45 weight-%. The term is frequently used interchangeably with ultramafic. Although most ultrabasic rocks are also ultramafic, there are some exceptions.
A basic rock is an igneous rock with a silica content between 45% and 52% by weight, such as gabbro, dolerite or basalt. Basic rocks include most mafic rocks as well as other rocks (Mindat).

Felsic

Felsic rocks are light-coloured rocks containing an abundance of one or all of quartz, feldspar, feldspathoid and muscovite.

Pyroxenite

Pyroxenite is an ultramafic plutonic igneous rock with essential pyroxene and acessory olivine, hornblende, chromite, magnetite, ilmenite, biotite, garnet and apatite (SS).
Clinopyroxenite is a pyroxenite dominated by clinopyroxenes, and orthopyroxenite is dominated by orthopyroxenes (Mindat).

Jacupirangite

Jacupirangite is a variety of alkali pyroxenite consisting essentially of titanium-bearing augite with minor amounts of titanium-bearing magnetite, nepheline, apatite, perovskite and melanite garnet (Mindat).

Websterite

Websterite is a pyroxenite with >5% clinopyroxene and >5% orthopyroxene (Mindat).

Dunite

Dunite is an ultramafic plutonic igneous rock containing more than 90% of olivine.
The essential constituent is olivine.
Common but not essential constituents include magnetite and pyroxene.
Metadunite is a metamorphosed dunite.

Norite

Norite is a a mafic, plutonic igneous rock including more than 50% anorthite and very much more orthopyroxene than clinopyroxene. Accessory minerals include olivine, magnetite, ilmenite, apatite and chromite, with accidentals biotite, hornblende and cordierite (S&S p287(.
Melanorite is a dark coloured norite, and leuconorite is a light coloured norite.

Peridotite

Peridotite is an ultramafic plutonic igneous rock containing more than 40% of olivine.
The essential constituent is olivine.
Common but not essential constituents include pyroxene and chromite. Nickel ores are associated with norites (orthopyroxene-dominated gabbros) and peridotite.

Wehrlite

Wehrlite is a peridotite containing <5% hornblende, <5% orthopyroxene and >5% clinopyroxene (Mindat).

Lherzolite

Lherzolite is an ultramafic plutonic igneous rock composed of >40% olivine with subordinate <5% hornblende, >5% orthopyroxene and >5% clinopyroxene (Mindat).

Harzburgite

Harzburgite is a peridotite containing <5% hornblende, >5% orthopyroxene and <5% clinopyroxene; it consists essentially of olivine and enstatite or its variety bronzite (Mindat).

Kimberlite

Kimberlite is an ultramafic igneous rock.
Essential constituents are carbonates such as calcite, together with olivine, phlogopite and pyroxene.
Common but not essential constituents include monticellite, perovskite and pyrope.

Lamproite

Lamproite is an ultrapotassic mantle-derived volcanic or subvolcanic rock. It has low CaO, Al₂O₃, Na₂O, high K₂O/Al₂O₃, a relatively high MgO content and extreme enrichment in incompatible elements. Lamproites are geographically widespread yet are volumetrically insignificant (Wiki).

Lamprophyre

Lamprophyre is a mafic igneous rock.
Essential constituents are feldspars and biotite.
Common but not essential constituents include augite, olivine, hornblende, calcite, titanite, magnetite, ilmenite and siderite (SS).

Monchiquite

Monchiquite is a lamprophyre containing phenocrysts of olivine, clinopyroxene and typically biotite or amphibole, in a groundmass of glass or analcime, often highly altered. Nepheline or leucite may be present (Mindat).

Urtite

Urtite is a plutonic igneous rock consisting of over 70% nepheline, with some aegirine-augite but no feldspar (Mindat).

Porphyry

Porphyry is an igneous rock of any composition that contains conspicuous phenocrysts in a fine-grained groundmass (Mindat).

Olivinite

Olivinite is a term originally used for ore-bearing olivine rocks and later for plutonic igneous rock composed of olivine with pyroxene and/or amphibole. In the Russian Republic the term is used for olivine rocks with accessory magnetite to distinguish them from dunite, which contains accessory chromite (Mindat).

Melilitolite

Melilitolite is an ultramafic plutonic igneous rock consisting essentially of melilite, pyroxene and olivine. Now defined as a general term for plutonic rocks in the melilite-bearing rocks classification (Mindat).

Turjaite

Turjaite is a melilitolite with more than 10% nepheline but more melilite than nepheline (Mindat).

Emery

Emery is a dark granular rock used to make abrasive powder. It largely consists of corundum, mixed with other minerals such as the iron-bearing spinels hercynite and magnetite, and also rutile. (Wiki).

VOLCANIC IGNEOUS ROCKS

Rhyolite

Rhyolite is a fine-grained feldspar-rich volcanic igneous rock, formed from a silica-rich magma. It contains
80 - 100% light minerals of which quartz is 20 - 60% and feldspars 40 - 80%.
Of the feldspars 35 - 100% are K-feldspars and 0 - 65% are plagioclase feldspars (albite to anorthite).
It also contains 0 - 20% dark minerals.
Essential constituents are K-feldspars, plagioclase feldspars and quartz.
Common but not essential constituents include amphibole, biotite and pyroxene. Rhyolite mainly occurs as lava domes (domes resulting from the slow extrusion of viscous lava from a volcano). Rhyolite, like granite, is most commonly associated with island arc (a chain of volcanic islands, parallel with and close to a boundary between two converging tectonic plates) and mountain-building magmatism.
Metarhyolite is metamorphosed rhyolite.

Dacite

Dacite is a volcanic igneous rock.
Essential constituents are plagioclase feldspars, quartz, biotite and hornblende.
Accessories are magnetite, ilmenite, sanidine, pyroxene and glass. (S&S)

Rhyodacite

Rhyodacite is a rock intermediate between rhyolite and dacite, containing >10% quartz and subequal amounts of plagioclase and K-feldspar. The extrusive equivalent of granodiorite. The principal minerals, sodic plagioclase, K-feldspar, quartz, and biotite or hornblende, commonly occur as phenocrysts in a finely crystalline groundmass of feldspar and quartz. Accessory minerals are apatite and magnetite, and occasionally augite (Mindat).

Latite

Latite is a volcanic igneous rock.
Essential constituents are sanidine, plagioclase feldspars, augite and hornblende.
Accessories are anorthoclase, olivine, feldspathoids, magnetite and ilmenite (S&S)

Trachyte

Trachyte is a feldspar-rich volcanic igneous rock of intermediate silica content. It contains
60 - 100% light minerals of which feldspars are 80 - 100% and quartz 0 - 20% or feldspathoids 0 - 10%.
Of the feldspars 35 - 65% are K-feldspars and 35 - 65% are plagioclase feldspars (albite to anorthite).
It also contains 0 - 40 % dark minerals.
Essential constituents are albite variety oligoclase and sanidine.
Common but not essential constituents include biotite, hornblende, nepheline, pyroxene and quartz.
Trachyte is most commonly associated with ocean island (islands without any foundation of continental rock, usually formed as the result of volcanic action) and continental rift (where the continental crust is thinning due to the underlying plates moving apart) magmatism.

Trachybasalt

Trachybasalt is an alkaline/basic extrusive rock intermediate in composition between trachyte and basalt, characterised by the presence of both calcic plagioclase and K-feldspar, along with clinopyroxene, olivine, and possibly minor analcime or leucite (Mindat).

Andesite

Andesite is a volcanic igneous rock with intermediate silica content. It contains
60 - 85% light minerals of which 80 - 100% are feldspars and 0 - 20% are quartz or 0 - 10% are feldspathoids.
Of the feldspars 65 - 100% are plagioclase feldspars and 0 - 35% are K-feldspars.
It also contains 15 - 40% dark minerals.
Essential constituents are plagioclase feldspars.
Common but not essential constituents include biotite, hornblende, and pyroxenes.
Andesite occurs in lava flows together with basalt and trachyte.

Propylite

Propylite is a hydrothermally altered rock, often andesite, resembling a greenstone and containing calcite, chlorite, epidote, quartz, and minor pyrite or iron oxides. Propylite is common in mining districts of the Western United States, generally in the outermost subzone of hydrothermal alteration (Mindat).

Hawaiite

Hawaiite is a sodium-rich dark coloured volcanic rock, intermediate between basalt and trachyte (Mindat).

Basalt

Basalt is a silica-poor volcanic igneous rock, formed from a silica-poor magma. It contains
30 - 60% light minerals of which feldspars are 80 - 100% and quartz 0 - 20% or feldspathoids 0 - 10%.
Of the feldspars 65 - 100% are plagioclase feldspars and 0 - 35% are K-feldspars.
It also contains 40 - 70% dark minerals.
Essential constituents are plagioclase feldspar and pyroxenes.
Common but not essential constituents include feldspathoids, olivine and quartz
In addition, many hydrothermal minerals are found filling cavities in basalt

Metabasalt

Metabasalt is a metamorphically altered basalt

Tholeiite

Tholeiite is a variety of basalt which is saturated or slightly oversaturated in silica with respect to alkalis, characterised by the presence of orthopyroxene and/or pigeonite in addition to clinopyroxene and calcic plagioclase (Mindat).

Komatiite

Komatiite is a variety of ultramafic lava that crystallises from high temperature magmas with 18% to 32% MgO. It often forms pillows and has chilled flow-tops and usually display well-developed spinifex textures with intergrown skeletal and bladed olivine and pyroxene crystals set in abundant glass (Mindat).

Nephelinite

Nephelinite is a fine-grained or porphyritic volcanic rock, of basaltic character, but primarily composed of nepheline and clinopyroxene, and lacking olivine and feldspar (Mindat).

Basanite

Basanite is a fine grained, very silica-poor, basaltic rock, with felsics comprising 10-60% feldspathoids and alkali feldspar/total feldspar <0.1, >10% olivine (Mindat).

Picrite

Picrite is a volcanic igneous rock with 1% to 2% (Na₂O+K₂O). Common but not essential constituents are olivine and pyroxene (Mindat).

Tephrite

Tephrites are a group of volcanic igneous rocks, of basaltic character, primarily composed of calcic plagioclase, augite, and nepheline or leucite as the main feldspathoids, with accessory K-feldspar (Mindat).

Phonolite

Phonolite is a volcanic igneous rock, with K-feldspar greater than 90% of the total feldspar (Mindat).
An essential component is sanidine.
Common but not essential components include nepheline, riebeckite, arfvedsonite, aegirine and diopside.
Accessories include albite, titaniferous augite, aenigmatite, apatite, titanite, magnetite, ilmenite, leucite, hauyne, sodalite, analcime, zeolites, andradite variety melanite and cancrinite (S&S, Mindat).

Tephritic-phonolite

Tephritic-phonolite is a phonolite with felsics comprising 60-90% feldspathoids and alkali feldspar/total feldspar 0.9-0.5. It is an uncommon, highly alkaline volcanic or sub-volcanic rock, mostly found in dykes (Mindat).

Tinguaite

Tinguaite is a variety of phonolite consisting of K-feldspar, nepheline with or without other feldspathoids, aegirine and sometimes biotite. It is characterized by "tinguaitic texture" in which needles of aegirine occur interstitially in a mosaic of K-feldspar and feldspathoids (Mindat).

Obsidian

Obsidian is a volcanic igneous rock with a variable composition. It is a glass formed by the rapid cooling of viscous granitic magma. It is very common in recent lava flows. Accessories include magnetite, ilmenite and feldspar as phenocrysts (S&S 314).

Vitrophyre

Vitrophyre is a volcanic rock with a porphyritic texture in which larger crystals are embedded in a glassy groundmass (Wiki).

Hyaloclastite

Hyaloclastite is a consolidated pyroclastic rock composed of angular fragments of glass which may or may not be devitrifed. (Mindat).

Scoria

Scoria is a highly vesicular basalt or basaltic glass.

Paralava

Paralava, or parabasalt, is a pyrometamorphic rock that is vesicular, aphanitic, often ropy and with clear flow structures, formed from melting of shale, sandstone or marl, resembling basalt or industrial slag. Typical constituents are olivine, pyroxene, calcium-rich plagioclase and hercynite (Mindat).

Pumice

Pumice is a volcanic rock that consists of highly vesicular rough textured volcanic glass, which may or may not contain crystals. It is typically light coloured (Wiki).

CLASTIC SEDIMENTARY ROCKS

Breccia

Breccia is a coarse-grained clastic sedimentary rock, composed of angular broken rock fragments held together by a mineral cement or in a fine-grained matrix; it differs from conglomerate in that the fragments have sharp edges and unworn corners (Mindat)

Conglomerate

Conglomerate is coarse-grained clastic sedimentary rock, composed of rounded to subangular fragments larger than 2 mm in diameter, set in a fine-grained matrix of sand or silt (Mindat).

Agglomerate

Agglomerate is a coarse accumulation of large blocks of volcanic material that contains at least 75% bombs. Volcanic bombs differ from volcanic blocks in that their shape records fluidal surfaces, such as ropy, ribbon, ragged, or amoeboid shapes (Wiki).

Sandstone

Sandstone is a clastic sedimentary rock comprised mainly of sand-sized grains, between 0.0625 and 4 mm across. The grains can be quartz, feldspar or rock fragments. Sandstone is deposited by a wide range of processes including river and stream deposits (fluvial), floodplain or river delta deposits (alluvial), windborn deposits (aeolian) and under-water, sediment-laden currents (turbidity currents).
Essential constituents are feldspars and quartz.
A common constituent is calcite

Arenite

Arenite is a clastic sedimentary rock with sand grain size between 0.0625 mm and 2 mm and containimg less than 15% fine-grained interstitial material (Wiki, Mindat).

Siltstone

Siltstone is a clastic sedimentary rock comprised mainly of grains sized 0.0039 to 0.0625 mm across.

Mudstone

Mudstone is a clastic sedimentary rock comprised mainly of grains sized less than 0.0039 mm across. Shale, clay and marl are types of mudstone. The majority of grains in mudstones are clay minerals such as montmorillonite and kaolinite.
Argillite is a mudstone with variable amounts of silt-sized particles composed predominantly of indurated clay particles.
Pelite is mudstone.

Metamudstone

Metamudstone (metapelite) is a metamorphosed mudstone (Mindat).

Shale

Shale is a mudstone with a fissile parting. It is the most abundant clastic sedimentary rock in the Earth's crust, comprising about 70% of sedimentary rocks. It consists of a high percentage of clay minerals, substantial amounts of quartz and smaller amounts of carbonates, feldspar, fossils and organic matter. Shale is coloured red and purple by hematite and goethite, blue, green and black by ferrous iron, and grey or yellowish by calcite.
It is deposited by gentle currents on deep ocean floors, shallow sea basins and river floodplains.
Metashale is a metamorphosed shale.
Black shale is a shale with at least 1% carbonaceous material indicating a reducing environment (Mindat).

Clay

Clay is a soft, cohesive, water-rich mudstone that is plastic when wet and hardens when fired. The majority of clays are largely composed of phyllosilicates, such as chlorite, kaolinite, mica, montmorillonite and muscovite variety illite.

Bentonite

Bentonite is an impure clay, primarily montmorillonite (Mindat).

Kaolin

Kaolin is a claystone rich in kaolinite. Lithomarge is a compact, massive form of kaolin (Mindat).

Arkose

Arkose is a clastic sedimentary rock containing at least 25% feldspar. The grains are mainly feldspar, with a little quartz, biotite, muscovite, and other minerals. The cement may be silicate (quartz or muscovite variety illite), calcitic or limonitic (S&S).

Graywacke

Graywacke is a clastic sedimentary rock; the clasts consist of quartz, feldspar and rock fragments in almost equal amounts; the matrix and the cement are clayey or chloritic, with iron oxides and hydroxides (S&S).

Marl

Marl is a mudstone containing a great deal of carbonate.
The essential constituent is calcite.
Common but not essential constituents include dolomite and hematite.

Turbidite

Turbidite is a sediment or rock deposited from, or inferred to have been deposited from, a turbidity current. It is characterized by graded bedding, moderate sorting, and well-developed primary structures (Mindat).

Tuff

Tuff is a fine-grained pyroclastic rock, ie it is formed by the lithification of beds of volcanic ash and lava fragments. Ignimbrite is a form of hardened tuff.

Laterite

Laterite is a red residual soil developed in humid, tropical, and subtropical regions of good drainage. It is leached of silica and contains concentrations particularly of iron oxides and hydroxides and aluminum hydroxides. It may be an ore of iron, aluminum, manganese or nickel.

CHEMICAL SEDIMENTARY ROCKS

Rocksalt

Rocksalt is the massive rock form of the mineral halite. It is a monomineralic chemical sedimentary rock.
The essential constituent is halite, and a common but not essential constituent is anhydrite.
Rock salt often occurs in salt domes. A salt dome is a structural dome formed when a thick bed of evaporite minerals found at depth intrudes vertically into surrounding rock strata. Salt domes contain anhydrite, gypsum, and native sulphur, in addition to halite and sylvite. Rocksalt forms from the evaporation of ocean or saline lake waters. It is rarely found at the Earth's surface, except where the climate is very arid.

Gypsum rock

Gypsum rock is a monomineralic chemical sedimentary rock with gypsum as its major constituent.
Common minor constituents are anhydrite, rocksalt, limestone and dolomite.
Gypsum rock originates by precipitation as sea water is evaporated or by the hydration of anhydrite.

Anhydrite rock

Anhydrite rock is a monomineralic chemical sedimentary rock with anhydrite as its major constituent.
Medium constituents are gypsum, calcite, dolomite, clay minerals and bitumen.
Anhydrite rock originates by precipitation from sea water or diagenetically from gypsum as a result of high temperature and thick overburden in mountain ranges.

Ironstone

Ironstone is a sedimentary rock, either deposited directly as a ferruginous sediment or created by chemical replacement, that contains a substantial proportion of iron compounds.

Phosphorite

Phosphorite, phosphate rock or rock phosphate is a non-detrital sedimentary rock that contains high amounts of phosphate minerals.
Phosphorus makes up about 0.10 percent of the weight of Earth’s crust in the form of phosphate minerals and phosphorus-containing organic compounds. More than six hundred phosphorus-bearing mineral species are known; apatite is the most abundant group of these phosphates, comprising fluorapatite, chlorapatite and hydroxylapatite; apatite is found as an accessory mineral in all rock types, sedimentary, igneous and metamorphic, but it is also a main rock-forming mineral in rocks such as sedimentary phosphorites (R&M 98.2.171-177).

BIOGENIC SEDIMENTARY ROCKS

Limestone

Limestone is a biogenic sedimentary rock formed in marine environments. It may also be of chemical sedimentary origin.
The essential constituent is calcite.
Common but not essential constituents include aragonite and dolomite.
Chalk is a friable limestone.
Metalimestone is a metamorphosed limestone.

Jasperoid

Jasperoid is a dense, usually grey, chert-like siliceous rock, in which chalcedony or cryptocrystalline quartz has replaced the carbonate minerals of limestone or dolostone (Mindat).
Jasperoids commonly occur peripheral to sediment-hosted gold deposits (CM 58.1.85-97)

Travertine

Travertine is a hard, dense variety of tufa (Mindat).

Tufa

Tufa is a chemical sedimentary rock composed of calcium carbonate, formed by evaporation as a surficial, spongy, porous, semifriable incrustation around the mouth of a hot or cold spring or seep, or along a stream carrying calcium carbonate in solution, and exceptionally as a thick, bulbous, concretionary or compact deposit in a lake or along its shore. It may also be precipitated by algae or bacteria. The hard, dense variety is travertine. It is not to be confused with tuff (Mindat).

Dolostone

Dolostone is a biogenic sedimentary rock formed in marine environments and consisting of more than 50% dolomite.
Most dolostone did not originally form as dolostone, but instead formed from the alteration of limestone as magnesium-rich water moved through it, altering its calcite and aragonite into dolomite. The replacement may be only partial, and most dolostone is a mixture of dolomite and calcite.
The main exception to this secondary dolostone is the rare primary dolostone that forms as a relatively late product of seawater evaporation.
The essential constituent is dolomite, almost always accompanied by calcite.
Common but not essential constituents include ankerite.
Metadolostone is a metamorphosed dolostone.

Diatomite

Diatomite is a biogenic sedimentary rock composed of diatom skeletons, consisting of about 90% opal. Diatoms are microscopic, single-celled algae that live in marine or fresh water, with skeletons made of silicon dioxide. The remaining 10% is made up of aluminium and iron oxides.

Chert

Chert is a chemical sedimentary rock consisting almost entirely of chalcedony; it may be biochemical, or formed by replacement.
Biochemical chert is formed when the siliceous skeletons of marine plankton are dissolved during diagenesis (rock formation), with silica being precipitated from the resulting solution.
Replacement chert, such as petrified wood, forms when other material is replaced by silica.
Chert occurs as nodules in limestone and dolostone as a replacement mineral. Flint is a variety of chert that occurs in chalk or marl. Agate is a type of chert that forms through direct precipitation of silica in voids within a rock. Chert also occurs in thin beds, when it is a primary deposit, and in beds and lenses of diatomite.
The essential constituent is chalcedony.
Common but not essential constituents include opal and quartz.

Novaculite

Novaculite is a uniform, fine-grained hard rock mostly composed of extremely fine-grained to cryptocrystalline quartz. It is a variety of chert (Mindat).

Radiolarite

Radiolarite is a siliceous-rock composed predominantly of radiolaria and with porosity greater than 50% (Mindat).

CONTACT METAMORPHIC ROCKS

Hornfels

Hornfels is formed by contact metamorphism close to igneous intrusions at temperatures of 200 to 800^oC and low to high pressure.
Common but not essential constituents include andalusite, cordierite, hornblende and plagioclase feldspar.
Hornfels is a characteristic rock of the hornblende-hornfels, albite-epidote-hornfels and pyroxene-hornfels facies.

Calc-silicate rock

Calc-silicate rock is a metamorphic rock mainly composed of calcium-bearing silicate minerals such as diopside, grossular - andradite, clinozoisite - epidote and wollastonite, and containing less than 5% by volume of carbonate minerals (usually dolomite or calcite). It is formed by medium to high grade contact metamorphism of impure limestone or dolostone (SS, Mindat).
Essential constituents include calcite, wollastonite, garnet (grossular, andradite), plagioclase feldspar (anorthite), scapolite, monticellite, diopside, augite variety fassaite and pyroxene.
Common but not essential constituents include titanite, ilmenite, clintonite, humite and graphite.
Accidentals include anthophyllite, forsterite, olivine, phlogopite, periclase, brucite, fluorite, quartz, melilite, celsian, vesuvianite and zoisite (SS).

Marble

Marble is formed by regional or contact metamorphism of limestone or dolostone at temperatures above 570^oC and low to high pressure.
The essential constituent is calcite.
Common but not essential constituents include actinolite, diopside, dolomite and tremolite.

Skarn

Skarn is a metasomatic and contact metamorphic rock formed by the contact metamorphism of limestone when it is intruded by an igneous rock, often granite, at temperatures above 570^oC and at low pressure and also by metasomatism (addition of elements to country rocks from magmatic or hydrothermal fluids). Calc-silicate minerals are an expected consequence of this type of reaction (R&M 94.6.551).
The essential constituent is calcite and a common constituent is dolomite.
Exoskarn is a skarn formed at and outside the intrusion which produced it, and is an alteration of wall rocks, whereas endoskarn forms within the intrusive body itself.

Tactite

Tactites are a type of skarn. They are multimineralic carbonate rocks resulting from contact metamorphism and metasomatism (addition of elements to country rocks from magmatic or hydrothermal fluids).

REGIONAL METAMORPHIC ROCKS

Slate

Slate is a very fine-grained, foliated rock with a pervasive fissile cleavage (splitting along flat planes) due to alignment of phyllosilicates. It is produced by the regional metamorphism of clay-rich sediments, such as shale and mudstone at about 2 kbar pressure and 500^oC.
Essential constituents are feldspar, mica and quartz.
Common but not essential constituents include graphite and pyrite. Slate is typically grey to black in colour with a dull lustre, and sometimes green. It is formed by regional metamorphism of argillaceous (clay-rich) sediments.
Slate is a characteristic rock of the prehnite-pumpellyite, greenschist and blueschist facies. With increasing metamorphic grade slate transforms into phyllite.

Serpentinite

Serpentinite is a regional metamorphic rock formed mainly from ultramafic parent rocks (protoliths) at about 5 kbar pressure and 400^oC. It is a common component of oceanic crust at a convergent plate boundary where the oceanic crust is forced down beneath the continental crust. Serpentinite forms by the transformation of olivine and pyroxene in peridotite to serpentine. Relicts of olivine and pyroxene are often present in the serpentinite. Dehydration of serpentinite at high temperature produces talc, tremolite and forsterite.
The essential constituent is serpentine.

Metaserpentinite

Metaserpentinite is metamorphosed serpentinite.

Phyllite

Phyllite is formed by regional metamorphism of argillaceous (clay-rich) sediments, such as shale and mudstone, at about 5 kbar pressure and 400^oC. It is a characteristic rock of the greenschist facies, and it is also a rock of the amphibolite facies.
Essential constituents are biotite, chlorite and muscovite.
Common but not essential constituents include feldspar, graphite and quartz.

Quartzite

Quartzite is a high-temperature metamorphic rock produced by regional metamorphism of sandstone. It is composed mainly of quartz, with mica, kyanite and sillimanite as accessories. Metaquartzite is a granulose metamorphic rock consisting essentially of quartz.

Schist

Schist is formed by regional metamorphism of a wide range of fine-grained sediments, including argillaceous (clay-rich) and arenaceous (sandy) sediments, mixed silica-rich and carbonate sediments, and igneous rocks, at about 4 to 15 kbar pressure and 450 to 700^oC.
It is a characteristic rock of the greenschist and blueschist facies, and it is also a rock of the amphibolite facies.
Essential constituents are feldspar, usually albite or its variety oligoclase, mica and quartz.
Common but not essential constituents include actinolite, garnet, graphite, hornblende and kyanite.
Mica schists are derived mainly from argillaceous (clay-rich) protoliths, quartz- and feldspar-rich schists have protoliths with a more significant arenaceous (sandy) component, graphite schists typically form from carbon-rich argillaceous (clay-rich) sediments and calc-silicate schists form from clay-rich limestone or calcite-rich mudstone, and often contain diopside and wollastonite.

Greenschist

Greenschist is a schistose metamorphic rock whose green colour is due to the presence of chlorite, epidote or actinolite (Mindat).

Greisen

Greisen is a medium-temperature metamorphic rock resulting from the alteration of granite by hot vapour from magma. It is composed mostly of light-coloured mica and quartz, commonly with topaz, fluorite and tourmaline as accessories.

Gneiss

Gneiss is a metamorphic rock formed by high grade regional metamorphism of rocks containing quartz and feldspar at about 6 kbar pressure and 700^oC. It is a characteristic rock of the granulite facies and it is also a rock of the amphibolite facies.
The precursor rock (original rock before metamorphism) may be granite, granodiorite, silica-rich igneous volcanic rocks, mudstone, siltstone or shale.
Common but not essential constituents include amphibole, feldspar, mica and quartz.
Flaser gneiss is a a dynamically metamorphosed rock in which lenses or layers of original or relatively unaltered granular materials are surrounded by a matrix of highly sheared and crushed material, giving the appearance of a crude flow structure (https://mrdata.usgs.gov/catalog/term-simple.php?term=6.6&thcode=4).

Orthogneiss

Orthogneiss is a gneiss formed by the metamorphism of an igneous rock.

Paragneiss

Paragneiss is a gneiss formed by the metamorphism of a sedimentary rock.

Amphibolite

Amphibolite is a metamorphic rock formed by regional metamorphism of silica-poor igneous rocks such as gabbro, at temperatures 500 - 750^oC and pressure 8 - 70 kbar (medium-grade metamorphism).
Essential constituents are amphiboles such as hornblende, tremolite and actinolite, and plagioclase feldspar (albite to anorthite).
Common but not essential constituents include epidote, garnet, biotite, clinopyroxene, scapolite, quartz and titanite.
Amphibolite is the characteristic rock of the amphibolite facies.

Migmatite

Migmatite is a banded metamorphic rock, typically consisting of darker bands rich in mafic minerals and lighter quartzofeldspathic parts (Mindat). It is formed by the remelting of the felsic component of a granitic rock in a water-saturated regional metamorphic environment. It is a mineral of the amphibolite facies (SS).
Essential components are quartz, K-feldspar, plagioclase feldspar and biotite. Accessories include zircon, apatite and magnetite. Accidentals include muscovite, cordierite, sillimanite, garnet and amphibole (SS).

Mylonite

Mylonite is a fine-grained, compact metamorphic rock produced by dynamic recrystallisation of the constituent minerals resulting in a reduction of the grain size of the rock. Mylonites can have many different mineralogical compositions; it is a classification based on the textural appearance of the rock (Wiki).

Granulite

Granulite is a metamorphic rock formed by high-grade regional metamorphism of silica-poor igneous and sedimentary rocks at temperature 500 - 750^oC, pressure 8 - 70 kbar.
It is the characteristic rock of the granulite facies.
Essential minerals are feldspars.
Common but not essential minerals include cordierite, amphibole, quartz and pyroxene.

Eclogite

Eclogite is a mafic rock formed by regional metamorphism at about 20 kbar pressure and 700^oC.
Essential constituents are omphacite and pyrope.
Common but not essential constituents include kyanite, paragonite, pyroxene, quartz and rutile.

Fenite

Fenite is a high temperature metamorphic rock.
Essential constituents are alkaline pyroxene, feldspar and sodium-rich amphibole.
Common but not essential constituents include apatite, calcite, nepheline, biotite, phlogopite and titanite (Mindat).

CONTACT METAMORPHIC ROCKS

Rodingite

Rodingite is a metasomatic metamorphic rock of the greenschist facies, derived by contact metasomatism of peridotite in the process of serpentinisation (SS).
Essential constituents are chlorite, garnet (grossular, andradite) and pyroxene (diopside, augite variety fassaite). Accessories are titanite and titanium-bearing clinohumite. Accidentals include amphibole, vesuvianite and epidote (SS).

OTHER

Metapyroxenite

Metapyroxenite is a metamorphic rock formed by the metamorphism of picrite (Mindat).

Chromitite

Chromitite is an igneous rock consisting of at least 90% chromite or magnesiochromite, usually with olivine and/or serpentine (Mindat).

Saprolite

Saprolite is a soft, earthy, typically clay-rich, thoroughly decomposed rock, formed in place by chemical weathering of igneous, sedimentary and metamorphic rocks. It often forms a layer or cover as much as 100 m thick, especially in humid and tropical or subtropical climates; the color is commonly some shade of red or brown, but it may be white or gray. Saprolite is characterised by preservation of structures that were present in the unweathered rock (Mindat).

Phoscorite

Phoscorite is a rock composed primarily of magnetite, apatite and olivine, usually associated with carbonatites (Mindat).

Metasomatite

Metasomatite is a rock produced by the process of practically simultaneous capillary solution and deposition by which a new mineral of partly or wholly different chemical composition may grow in the body of an old mineral or mineral aggregate. The presence of interstitial, chemically active pore liquids or gases contained within a rock body or introduced from external sources is essential for the replacement process, that often, though not necessarily, occurs at constant volume with little disturbance of textural or structural features (Mindat).

Ophiolite

Ophiolite is an igneous rock consisting largely of serpentine, believed to have been formed from the submarine eruption of oceanic crustal and upper mantle material (Wiki).

Aphanite

Aphanites are igneous rocks that are so fine-grained that their component mineral crystals are not visible to the naked eye. This geological texture results from rapid cooling in volcanic or hypabyssal environments (Wiki).

Asphaltite

Asphaltite is rock rich in bitumen (Mindat).

Banded iron formation

Banded iron formations are iron-rich rocks that typically consist of repeated, thin iron oxide layers, a few mm to a few cm in thickness, but they may be banded from a microscopic to a metre scale. The oxide bands are dark grey to black magnetite or hematite, alternating with bands of iron-poor shales and cherts, usually red in colour, of similar thickness, or iron rich silicates and carbonates, including siderite, ankerite, riebeckite, stilpnomelane and minnesotaite (Mindat).

Itabirite

Itabirite is a laminated, metamorphosed oxide-facies iron formation in which (1) the original chert or jasper bands have been recrystallized into megascopically distinguishable grains of quartz and (2) the iron is present as thin layers of hematite, magnetite or martite (Mindat).

Trachyandesite

Trachyandesite is a fine-grained, usually extrusive, alkaline/basic rocktype intermediate between basaltic andesite and phonolite (Mindat).

Shoshonite

Shoshonite is a rock composed of olivine and augite phenocrysts in a groundmass of labradorite with K-feldspar rims, olivine, augite, a small amount of leucite and some dark-coloured glass (Mindat).

Benmoreite

Benmoreite is a silica-undersaturated volcanic rock of intermediate composition. It is a sodium-rich variety of trachyandesite and belongs to the alkalic suite of igneous rocks (Wiki).

Lapis-lazuli

Lapis-lazuli is an uncommon metamorphic rock having lazurite as an essential component (Mindat).

Lydite

Lydite is a sedimentary silica-rich rock belonging to the group of organogenic rocks, formed mostly from radiolaria, and is black or dark grey, cryptocrystalline or very finely crystalline. It consists mainly of chalcedony and/or microcrystalline quartz with minor organic matter and often trace pyrite. The fluctuating content of clay minerals and pyroclastic components commonly causes strong layering. During diagenesis, as a result of chalcedony recrystallization and remobilisation, quartz may infill the porosity and form veins, while the organic components are highly carbonised (Mindat).

Tourmalinite

Tourmalinite is a rock that mostly consists of often very fine-grained, dark tourmaline, usually formed by hydrothermal replacement of feldspar, mica and other minerals. Tourmalinites are by definition stratabound rocks containing ≥ 20 volume % of tourmaline (Mindat).

Trap rock

Trap rock is any dark-coloured, fine-grained, non-granitic intrusive or extrusive igneous rock (Wiki).

Calcrete

Calcrete is a calcareous duricrust, caliche or calcitic conglomerate consisting of surficial sand and gravel cemented into a hard mass by calcium carbonate precipitated from solution and redeposited through the agency of infiltrating waters, or deposited by the escape of carbon dioxide from vadose water (Mindat).

Caliche

"Caliche" mostly refers to a reddish brown to white calcareous material of secondary accumulation, commonly found in layers on or near the surface of stony soils of arid and semiarid regions, but also occurring as a subsoil deposit in subhumid climates. It may occur as a thin, friable horizon within the soil, but more commonly it is up to a metre or more in thickness, impermeable and strongly indurated. It is composed largely of a calcareous cement, in addition to such materials as gravel, sand and mud. Roughly equivalent to calcrete.
A name of spanish language origin that means different things in different places. In Chile it is used for the nitrate bed ores (principally but not exclusively nitratine). Andean sulphur miners sometimes use it for white sulphate crusts created by acid fumarolic alteration of volcanic rocks. In the American Southwest this name is also commonly used to refer to crusts of carbonate (calcite) recently deposited on rocks and in seams, and as a term for soils in semi-arid areas that have become indurated by interstitial carbonate deposition (Mindat).

Hornblendite

Hornblendite is an ultramafic plutonic rock composed almost entirely of hornblende. (Mindat).

Anatexite

Anatexite is a rock still showing the evidence of in situ formation by anatexis. Anatexis is the melting of pre-existing rock (Mindat).

Silexite

Silexite is an igneous rock composed essentially of primary quartz (60% to 100%), for example, a quartz dike, segregation mass, or inclusion inside or outside its parent rock (Mindat).

Natrocarbonatite

Natrocarbonatite is a carbonatite composed essentially of sodium +/-potassium +/-calcium carbonate minerals. A lava known from only one locality currently (July 2024). (Mindat).

Jadeitite

Jadeitite is a metamorphic rock found in blueschist facies metamorphic terrains, in isolated metasomatically altered bodies within serpentinite associated with subduction zone environments; it consists almost entirely of jadeite pyroxene (Mindat).

Colluvium

Colluvium is a general name for loose, unconsolidated sediments that have been deposited at the base of hillslopes by either rainwash, sheetwash, slow continuous downslope creep, or a variable combination of these processes. It is typically composed of a heterogeneous range of rock types and sediments ranging from silt to rock fragments of various sizes (Mindat).

Pyroclastic-rock

Pyroclasic-rock is rock composed of volcanic fragments derived from explosive volcanic activity (Mindat).

Argillite

Argillite is a compact rock derived either from mudstone (claystone or siltstone), or shale, that has undergone a somewhat higher degree of induration than mudstone or shale but is less clearly laminated and without its fissility, and that lacks the cleavage distinctive of slate (Mindat).

Pyroclastic-rock

Pyroclasic-rock is rock composed of volcanic fragments derived from explosive volcanic activity (Mindat).

Pulaskite

Pulaskite is a variety of nepheline-bearing alkali feldspar syenite containing varying amounts of sodic pyroxenes and amphiboles, fayalite, biotite and minor amounts of nepheline (Mindat).

Metacarbonate

Metacarbonate forms by metamorphism of sedimentary protoliths that contain significant amounts of carbonate minerals.

Oolite

Oolite is a sedimentary rock, usually a limestone, made up chiefly of ooliths (small round or ovate accretionary body, resembling the roe of fish) cemented together (Mindat).