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Rockhound rock identification guide – how to identify rocks and minerals for rockhounds and new rock hunters.

Rocky side of a mountain

Learning how to identify rocks and minerals can be a rewarding hobby and a useful skill for hiking, camping, and survival. Rock hunting can deepen your understanding of geology and the earth’s history, and of course, it is fun. Those science-minded nerds who love to collect rocks are called “rockhounds“.

A rockhound is a person who is interested in collecting rocks and minerals as a hobby. They might go out into the field to collect specimens or visit rock and mineral shows, searching for rare rocks, minerals, and gemstones to add to their collection. Some rockhounds might also be interested in lapidary, the art of cutting, shaping, and polishing stones. Some simply appreciate the natural beauty of rocks and minerals.

Use this Rockhound rock identification guide to help you identify rocks and minerals. Learn the types of rocks and general characteristics rock hounds use to identify a rock. Then run through our free rock identification guide to pinpoint your find.

Let Geek Slop know if you have any suggested additions to the guide, and of course, forward us your photos to add to the photo gallery.

Step 1 – Identify the type of rock

To identify a rock, a rockhound must first determine the type of rock – is it igneous, sedimentary, or metamorphic?

Igneous rocks

Rockhounds rock mineral guide - Examples of igneous rocks

Igneous rocks like granite or lava are hard, uniform rocks with a smooth surface, possibly even a glassy texture. They usually have black, white, and/or gray minerals.

Igneous rocks are formed from the cooling and solidification of magma or lava. Magma is molten rock that is found beneath the Earth’s surface, while lava is molten rock that has erupted onto the Earth’s surface. When magma or lava cools and solidifies, it forms igneous rocks. The type of igneous rock that forms depends on the rate of cooling and the chemical composition of the magma or lava.

Igneous rocks are further classified into intrusive and extrusive rocks depending on whether they cool and solidify beneath the earth’s surface or on top of it. Intrusive rocks, also known as plutonic rocks, are formed through the slow cooling and solidification of magma deep within the Earth’s crust. They are typically coarse-grained and have a crystalline structure. Examples of intrusive rocks include granite, diorite, and gabbro. Rockhounds usually find igneous rocks in mountainous areas or within the cores of continents.

Extrusive rocks, also known as volcanic rocks, are formed through the rapid cooling and solidification of lava on the Earth’s surface. They often have a fine-grained texture and may contain air pockets or vesicles. Examples of extrusive rocks include basalt, pumice, and obsidian. These rocks are usually found near volcanic areas or within regions of tectonic activity.

Examples of igneous rocks

Examples of igneous rocks include:

  • Basalt
  • Obsidian
  • Pumice
  • Andesite
  • Dacite
  • Rhyolite
  • Granite
  • Gabbro
  • Peridotite
  • Scoria
  • Tuff
  • Phonolite
  • Trachyte
  • Komatiite
  • Kimberlite
  • Nephelinite
  • Carbonatite
  • Aplite

Sedimentary rocks

Rockhound rock mineral guide - Examples of Sedimentary rocks

Sedimentary rocks like limestone or shale are rocks made from sediment that has hardened. They have sandy or clay-like layers and are usually brown to gray in color. Sometimes, they have fossils and marks from wind or water.

Sedimentary rocks are formed from the accumulation of sediment over time. Sediment consists of pieces of rock, mineral fragments, shells, and other debris that are transported by water, wind, or ice. As the sediment is deposited and compacted, it forms layers that eventually harden into rock.

Rockhounds usually find sedimentary rocks near bodies of water such as rivers, lakes, and oceans. They can also be found in areas where there has been a lot of volcanic activity or windy areas where sediment has accumulated over time.

Examples of sedimentary rocks

Examples of sedimentary rocks include:

  • Sandstone
  • Shale
  • Limestone
  • Conglomerate
  • Siltstone
  • Mudstone
  • Arkose
  • Chert
  • Coquina
  • Dolomite
  • Breccia
  • Evaporite
  • Greywacke
  • Micrite
  • Oolite
  • Travertine
  • Tufa
  • Ironstone
  • Coal

Metamorphic rocks

Rockhound rock mineral guide - Examples of Metamorphic rocks

Metamorphic rocks like marble are hard, with layers of light and dark minerals and a foliated texture. They come in various colors and often contain glittery mica.

Metamorphic rocks are formed from the transformation of existing rocks due to heat, pressure, or chemical reactions. These rocks are formed when existing rocks are subjected to high temperatures and pressure, which causes them to change their physical and chemical properties. The transformation can also occur due to chemical reactions with fluids that flow through the rock.

Metamorphic rocks can be classified into foliated and non-foliated rocks, depending on whether they have a layered or banded appearance. Foliation is a common feature of metamorphic rocks that is caused by the application of pressure and heat during the rock’s formation. This process causes the minerals within the rock to realign themselves, forming a layered or banded appearance.

Foliated rocks are types of metamorphic rocks that have been subjected to heat and pressure, causing them to develop a layered or banded appearance. Slate, schist, and gneiss are examples of foliated rocks. Slate is a fine-grained rock that is formed from the metamorphism of shale, while schist is a coarse-grained rock that is formed from the metamorphism of mudstone or shale. Gneiss is a high-grade metamorphic rock that is formed from the metamorphism of granite or other igneous rocks.

Non-foliated rocks, on the other hand, lack the layered or banded appearance of foliated rocks. They are typically formed from a single mineral or mineral type. Marble and quartzite are examples of non-foliated rocks. Marble is a metamorphic rock that is formed from the metamorphism of limestone or dolomite, while quartzite is formed from the metamorphism of sandstone.

Rockhounds most often find metamorphic rocks in areas where there are high amounts of geological activity such as mountain ranges or areas with high levels of tectonic activity.

Examples of metamorphic rocks

Examples of metamorphic rocks include:

  • Gneiss
  • Marble
  • Quartzite
  • Schist
  • Slate
  • Amphibolite
  • Blueschist
  • Eclogite
  • Granulite
  • Hornfels
  • Migmatite
  • Phyllite
  • Skarn
  • Soapstone
  • Anthracite
  • Serpentinite

Step 2 – Determine the rock’s basic characteristics

Once you’ve determined the type of rock, check the rock’s grain size and hardness. These are the most important characteristics of rock identification for a rockhound.

Rock grain size

If the grains are visible without a magnifier, it’s considered coarse. They are considered fine if they are small enough to require a magnifier to see them. The table below has the grain size names and measurements to use when identifying a rock type.

SizeDiameter (mm)Grain size name
Smaller1/256Clay (indistinguishable)
Rock and mineral grain size nomenclature with examples

Rock hardness

Rock hardness is measured using the Mohs scale and refers to the hardness of the minerals within the rock. Hard rock scratches glass and steel, usually signifying the minerals quartz or feldspar are present. Soft rock doesn’t scratch steel but will scratch fingernails, while very soft rock won’t even scratch fingernails.

Rockhounds use fingernails, coins, knife blades, steel files, glass, and other rocks and minerals to test the hardness of a rock or mineral. The table below illustrates the Mohs’ hardness scale (the numerical value in column 2), how to determine the Mohs’ hardness value, and an example of the mineral that represents the Mohs’ hardness.

MineralHardnessHow to Test
Talc1Can be scratched by a fingernail
Gypsum2Can be scratched by a fingernail, or scratched by a copper coin
Calcite3Can be scratched by a copper coin, or scratched by a steel knife
Fluorite4Can be scratched by a steel knife, or scratched by a small piece of quartz
Apatite5Can be scratched by a small piece of quartz, or scratched by a steel file
Orthoclase feldspar6Can be scratched by a steel file, or scratched by a piece of window glass
Quartz7Can scratch window glass
Topaz8Can scratch quartz
Corundum9Can scratch topaz
Diamond10Can scratch all the minerals above
Mohs rock and mineral hardness scale with examples

Step 3 – use the appropriate rock identification chart for your rock type

Now that you’ve determined the rock type, grain size, and hardness, you are ready to begin pinpointing the specific rock or mineral. Use the rockhound rock identification charts below to help you identify your rock. Start with the table for your rock’s specific type. Pay attention to the color and composition of the rock’s grain. Test its hardness. Start in the left column of the appropriate table and work your way across.

Igneous Rock Identification

HardnessGrain SizeUsual ColorOtherCompositionRock Type
5-5.5finedarkglassy appearancelava glassObsidian
5-6finelightmany small bubbleslava froth from sticky lavaPumice
5-6finedarkmany large bubbleslava froth from fluid lavaScoria
6-7fine or mixedlightcontains quartzhigh-silica lavaFelsite
7fine or mixedmediumbetween felsite and basaltmedium-silica lavaAndesite
6fine or mixeddarkhas no quartzlow-silica lavaBasalt
5-7mixedany colorlarge grains in fine-grained matrixlarge grains of feldspar, quartz, pyroxene or olivinePorphyry
6-7coarselightwide range of color and grain sizefeldspar and quartz with minor mica, amphibole or pyroxeneGranite
6-7coarselightlike granite but without quartzfeldspar with minor mica, amphibole or pyroxeneSyenite
5-7coarselight to mediumlittle or no and quartz with dark mineralsTonalite
5-6coarsemedium to darklittle or no quartzlow-calcium plagioclase and dark mineralsDiorite
6-7coarsemedium to darkno quartz; may have olivinehigh-calcium plagioclase and dark mineralsGabbro
5.5-6.5coarsedarkdense; always has olivineolivine with amphibole and/or pyroxenePeridotite
5-6coarsedarkdensemostly pyroxene with olivine and amphibolePyroxenite
5.5-6.5coarsegreendenseat least 90 percent olivineDunite
6-7very coarseany colorusually in small intrusive bodiestypically graniticPegmatite
Igneous Rock Identification

Sedimentary Rock Identification

HardnessGrain SizeCompositionOtherRock Type
hardcoarseclean quartzwhite to brownSandstone
hardcoarsequartz and feldsparusually very coarseArkose
hard or softmixedmixed sediment with rock grains and claygray or dark and “dirty”Wacke/Graywacke
hard or softmixedmixed rocks and sedimentround rocks in finer sediment matrixConglomerate
hard orsoftmixedmixed rocks and sedimentsharp pieces in finer sediment matrixBreccia
hardfinevery fine sand; no clayfeels gritty on teethSiltstone
hardfinechalcedonyno fizzing with acidChert
softfineclay mineralssplits in layersShale
softfinecarbonblack; burns with tarry smokeCoal
softcoarse or finedolomiteno fizzing with acid unless powderedDolomite rock
softcoarsefossil shellsmostly piecesCoquina
very softcoarsehalitesalt tasteRock Salt
very softcoarsegypsumwhite, tan or pinkRock Gypsum
Sedimentary Rock Identification

Metamorphic Rock Identification

HardnessFoliationGrain SizeUsual ColorOtherRock Type
1foliatedfinelightvery soft; greasy feelSoapstone
2-2.5foliatedfinedarksoft; strong cleavageSlate
2.5-4nonfoliatedfinedarksoft; massive structureArgillite
3-4foliatedfinedarkshiny; crinkly foliationPhyllite
5-7foliatedcoarsemixed dark and lightcrushed and stretched fabric; deformed large crystalsMylonite
6-7foliatedcoarsemixed dark and lightwrinkled foliation; often has large crystalsSchist
6-7foliatedcoarsemixeddistorted “melted” layersMigmatite
6foliatedcoarsedarkmostly hornblendeAmphibolite
2.5-5.5nonfoliatedfinegreenishsoft; shiny, mottled surfaceSerpentinite
2.5-3nonfoliatedfine or coarsedarkdull and opaque colors, found near intrusionsHornfels
6-7nonfoliatedcoarsered and greendense; garnet and pyroxeneEclogite
3-4nonfoliatedcoarselightsoft; calcite or dolomite by the acid testMarble
7nonfoliatedcoarselightquartz (no fizzing with acid)Quartzite
Metamorphic Rock Identification

A complete list of rocks by rock type

Below is an extensive list of rocks by rock type. A dedicated rockhound will become familiar with all the rocks in the lists. Once familiar with these rocks, a rockhound is able to easily and quickly identify a rock just by looking at it.

List of igneous rocks

Igneous rocksRock descriptionMohr’s hardnessDistinguishing properties
AdakiteVolcanic rock type6-7High Sr/Y ratio
AndesiteType of volcanic rock5-6Fine-grained, porphyritic texture
Alkali feldspar graniteType of igneous rock rich in alkali feldspar5-6Light-colored, coarse-grained texture
AnorthositeMafic intrusive igneous rock composed predominantly of plagioclase6-7Light-colored, coarse-grained texture
ApliteFine-grained intrusive igneous rock type similar to granite5-6Light-colored, fine-grained texture
BasaltMagnesium- and iron-rich extrusive igneous rock5-6Dark-colored, fine-grained texture
ʻAʻāMolten rock expelled by a volcano during an eruption – Basaltic lava with a crumpled appearance5-6Rough, sharp texture
PāhoehoeMolten rock expelled by a volcano during an eruption – Basaltic lava with a flowing, often ropy appearance5-6Smooth, ropy texture
Basaltic trachyandesite5-6Intermediate between basalt and andesite
MugeariteVolcanic rock type5-6Alkali basalt
ShoshonitePotassium-rich variety of basaltic trachyandesite5-6High K2O/Na2O ratio
BasaniteType of volcanic rock5-6Dark-colored, fine-grained texture
BlairmoriteRare porphyritic volcanic rock4-5Porphyritic texture, high Al2O3 content
BoniniteUltramafic extrusive rock high in both magnesium and silica5-6High MgO content
CarbonatiteIgneous rock with more than 50% carbonate minerals3.5-4Contains more than 50% carbonate minerals
CharnockiteType of granite containing orthopyroxene6-7Coarse-grained texture, high Na2O/K2O ratio
EnderbiteIgneous rock of the charnockite series6-7Coarse-grained texture, high Na2O/K2O ratio
DaciteVolcanic rock intermediate in composition between andesite and rhyolite6-7Intermediate between andesite and rhyolite
Diabase, also known as doleriteType of igneous rock6Dark-colored, fine-grained texture
DioriteIgneous rock type6-7Coarse-grained texture
Napoleonite, also known as corsiteVariety of diorite with orbicular structure6-7Orbicular structure
DuniteUltramafic and ultrabasic rock from Earth’s mantle which is made of the mineral olivine5-6High olivine content
EssexiteIgneous rock type6-7Intermediate between diorite and granite
FoidoliteIgneous rock rich in feldspathoid minerals5-6Rich in feldspathoid minerals
GabbroCoarse-grained mafic intrusive rock6-7Coarse-grained texture
GraniteCommon type of intrusive, felsic, igneous rock with a granular structure6-7Coarse-grained texture
GranodioriteType of coarse-grained intrusive igneous rock6-7Coarse-grained texture
GranophyreSubvolcanic rock that contains quartz and alkali feldspar in characteristic angular intergrowthsContains quartz and alkali feldspar
HarzburgiteUltramafic mantle rock5-6Coarse-grained texture
HornblenditePlutonic rock consisting mainly of the amphibole hornblendeConsists mainly of hornblende
HyaloclastiteVolcaniclastic accumulation or breccia
IcelanditeIgneous rock type5-6
IgnimbriteType of volcanic rock4-5
IjoliteIgneous rock consisting essentially of nepheline and augiteConsists of nepheline and augite
KimberliteIgneous rock which sometimes contains diamonds
KomatiiteUltramafic mantle-derived volcanic rock5-6
LamproiteUltrapotassic mantle-derived volcanic or subvolcanic rockUltrapotassic
LamprophyreUltrapotassic igneous rocks – An ultramafic, ultrapotassic intrusive rock dominated by mafic phenocrysts in a feldspar groundmassUltrapotassic
LatiteType of volcanic rock – A silica-undersaturated form of andesite5-6Silica-undersaturated
LherzoliteAn ultramafic and ultrabasic rock that is composed of olivine and pyroxene – An ultramafic rock, essentially a peridotite5-6Composed of olivine and pyroxene
MonzograniteA silica-undersaturated granite with <5% normative quartz6-7Silica-undersaturated
MonzoniteIgneous intrusive rock with low quartz and equal plagioclase and alkali feldspar – a plutonic rock with <5% normative quartz6-7Low quartz
Nepheline syeniteHolocrystalline plutonic rock – A silica-undersaturated plutonic rock of nepheline and alkali feldspar5-6Silica-undersaturated
NepheliniteIgneous rock made up almost entirely of nepheline and clinopyroxene – A silica-undersaturated plutonic rock with >90% nephelineSilica-undersaturated
NoriteIgneous rock – A hypersthene-bearing gabbro6-7Hypersthene-bearing
ObsidianNaturally occurring volcanic glass5-5.5
PegmatiteIgneous rock with very large interlocked crystalsVery large, interlocked crystals
PeridotiteCoarse-grained ultramafic igneous rock type5.5-6Dark green color, high density
PhonoliteUncommon extrusive rock – A silica-undersaturated volcanic rock; essentially similar to nepheline syenite5-6Fine-grained, light-colored, contains feldspathoids
PhonotephriteStrongly alkaline volcanic rock with a composition between phonolite and tephrite – A volcanic rock with a composition between phonolite and tephrite5-6Fine-grained, porphyritic texture
PicriteVariety of high-magnesium basalt that is very rich in the mineral olivine – An olivine-bearing basalt5-6Dark green color, high density, abundant olivine
PorphyryTextural form of igneous rock with large-grained crystals in a fine matrix6-7Porphyritic texture, often contains quartz and feldspar
PumiceLight colored highly vesicular volcanic rock5-6Very low density, often floats on water
PyroxeniteIgneous rock – a coarse-grained plutonic rock composed of >90% pyroxene5.5-6Dark color, abundant pyroxene
Quartz dioriteIgneous, plutonic rock – A diorite with >5% modal quartz6-7Light color, abundant quartz
Quartz monzoniteType of igneous rock – An intermediate plutonic rock, essentially a monzonite with 5–10% modal quartz6-7Light color, abundant quartz and feldspar
QuartzoliteExtremely rare igneous rock made mostly of quartz – An intrusive rock composed mostly of quartz7White or light-colored, composed mostly of quartz
RhyodaciteVolcanic rock rich in silica and low in alkali metal oxides – A felsic volcanic rock which is intermediate between a rhyolite and a dacite6-7Porphyritic texture, light color
RhyoliteIgneous, volcanic rock, of felsic (silica-rich) composition6Fine-grained, often contains quartz and feldspar
ComenditeHard, peralkaline igneous rock, a type of light blue-gray rhyolite6Light blue-gray color, peralkaline composition
PantelleritePeralkaline rhyolite type of volcanic rock6Light-colored, peralkaline composition
ScoriaDark vesicular volcanic rock5-6Porous texture, dark color
ShonkiniteIntrusive igneous rock – a plutonic rock5-6Dark color, composed of feldspar and pyroxene
SoviteIgneous rock – A coarse-grained carbonatite rock3-4Light color, composed of carbonate minerals
SyeniteIntrusive igneous rock – A plutonic rock dominated by orthoclase feldspar; a type of granitoid5-6Light color, composed of feldspar and mafic minerals
TachylyteForm of basaltic volcanic glass – Essentially a basaltic glass5.5-6Glassy texture, dark color
TephriphonoliteType of igneous rock – A volcanic rock with a composition between phonotephrite and phonolite5-6Fine-grained, contains feldspathoids
TephriteIgneous, volcanic rock – A silica-undersaturated volcanic rock5-6Low density, feldspathoid-bearing
TonaliteIgneous rock – A plagioclase-dominant granitoid6-7Plagioclase-dominant, coarse-grained
TrachyandesiteExtrusive igneous rock – An alkaline intermediate volcanic rock5-6Porphyritic, fine-grained
BenmoreiteVolcanic rock type – sodic trachyandesite5-6Porphyritic, fine-grained
TrachybasaltVolcanic rock – A volcanic rock with a composition between basalt and trachyte5-6Porphyritic, fine-grained
HawaiiteVolcanic rock – a sodic type of trachybasalt, typically formed by ocean island (hot spot) volcanism5-6Porphyritic, fine-grained
TrachyteExtrusive igneous rock – A silica-undersaturated volcanic rock; essentially a feldspathoid-bearing rhyolite5-6Porphyritic, feldspathoid-bearing
TroctoliteIgneous rock – A plutonic ultramafic rock containing olivine, pyroxene and plagioclase5-6Coarse-grained, olivine-rich
TrondhjemiteLight-colored intrusive igneous rock – A form of tonalite where plagioclase-group feldspar is oligoclase6-7Plagioclase-dominant, coarse-grained
TuffRock consolidated from volcanic ash1-2Porous, lightweight
WebsteriteUltramafic and ultrabasic rock – A type of pyroxenite, composed of clinoproxene and orthopyroxene5-6Coarse-grained, ultramafic
WehrliteUltramafic rock – An ultramafic plutonic or cumulate rock, a type of peridotite, composed of olivine and clinopyroxene5-6Coarse-grained, ultramafic

List of sedimentary rocks

Sedimentary rocksDescriptionMohr’s Hardness RatingDistinguishing Properties
ArgilliteSedimentary rock, mostly of indurated clay particles1-2Fine-grained, dark gray to black-colored rock
ArkoseType of sandstone containing at least 25% feldspar6-7Coarse-grained, reddish-brown colored rock
Banded iron formationDistinctive layered units of iron-rich sedimentary rock that are almost always of Precambrian age5.5-6.5Alternating bands of iron oxide and chert
BrecciaRock composed of broken fragments cemented by a matrix2.5-3Angular fragments of different rocks and minerals, cemented by finer-grained material
CalcareniteType of limestone that is composed predominantly of sand-size grains3Light-colored, composed mainly of sand-sized grains
ChalkSoft, white, porous sedimentary rock made of calcium carbonate1-2Soft and crumbly, white or gray-colored rock
ChertHard, fine-grained sedimentary rock composed of cryptocrystalline silica6.5-7Hard, brittle, usually gray-colored rock
ClaystoneClastic sedimentary rock composed primarily of clay-sized particles1-2Fine-grained, typically gray-colored rock
CoalCombustible sedimentary rock composed primarily of carbon1-2Hard, typically gray or black-colored rock
ConglomerateCoarse-grained sedimentary rock composed mostly of rounded to sub-angular fragments6-7Rounded or angular fragments of different sizes and types of rocks, cemented by finer-grained material
CoquinaSedimentary rock that is composed mostly of fragments of shells3Composed of broken shells and shell fragments, typically light-colored
DiamictiteType of sedimentary rock2.5-4Unsorted mixture of different sizes and types of rocks, with a matrix of finer-grained material
DiatomiteSoft, siliceous sedimentary rock that is easily crumbled5.5-6.5Light-colored, composed mainly of the silica shells of diatoms
Dolomite (rock), also known as DolostoneSedimentary carbonate rock that contains a high percentage of the mineral dolomite3.5-4Light-colored, typically granular or crystalline
EvaporiteWater-soluble mineral deposit formed by evaporation from an aqueous solution2.5-4Composed of minerals such as halite, gypsum, or anhydrite, formed by evaporation of water
FlintCryptocrystalline form of the mineral quartz7Coarse-grained, typically gray-colored rock
GeyseriteForm of opaline silica that is often found around hot springs and geysers5.5-6.5Formed from the precipitation of dissolved silica around hot springs and geysers
GreywackeHard, dark sandstone with poorly sorted angular grains in a compact, clay-fine matrix6-7Composed of angular fragments of different types of rocks, with a matrix of finer-grained material
GritstoneHard, coarse-grained, siliceous sandstone6-7Product of rock weathering in wet tropical climate rich in iron and aluminum
ItacolumitePorous sandstone known for flexibility2.5-3Composed of sand-sized grains that are loosely cemented together, allowing the rock to be flexible
JaspilliteBanded mixture of hematite and quartz6-7Alternating bands of red-colored hematite and gray-colored quartz
LateriteTypically gray-colored, composed of a mixture of calcium carbonate and clay minerals3-3.5Reddish-brown colored rock, formed from the weathering of other rocks in tropical regions
LigniteSoft, brown, combustible, sedimentary rock1-2Light-colored, composed of organic material such as peat
LimestoneSedimentary rocks made of calcium carbonate3-4Light-colored, composed mainly of calcium carbonate
MarlLime-rich mud or mudstone which contains variable amounts of clays and silt2-4Typically gray colored, composed of a mixture of calcium carbonate and clay minerals
MudstoneTypically gray-colored, composed of phosphate minerals such as apatite1.5-3Fine-grained, typically gray colored rock
Oil shaleOrganic-rich fine-grained sedimentary rock containing kerogen2-4Fine-grained sedimentary rock whose original constituents were clays or mud
OoliteSedimentary rock formed from ooids3.5-4Composed of small, spherical grains called ooids, typically light-colored
PhosphoriteSedimentary rock containing high amounts of phosphate minerals3.5-4Fine-grained, typically gray-colored rock that splits into thin layers
SandstoneClastic sedimentary rock composed mainly of sand-sized mineral particles or rock fragments6-7Fine-grained, typically gray-colored rock
ShaleFine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments (silt-sized particles) of other minerals, especially quartz and calcite3-4Coarse-grained, typically tan or brown-colored rock
SiltstoneSedimentary rock composed mainly of silt-sized particles6-7Coarse-grained, typically gray-colored rock composed of a mixture of different types of rocks and minerals
TravertineSedimentary rock, mostly of calcium carbonate, formed from the accumulation of mineral deposits from hot springs or streams4-5Light-colored, formed from the precipitation of calcium carbonate from water
TufaPorous limestone rock formed by precipitation of carbonate minerals from ambient temperature water bodies5-7Porous, light-colored rock formed from the precipitation of calcium carbonate from water
TurbiditeSedimentary deposit formed when gravity-driven downslope movement of fluidized, sediment-laden flow overcomes frictional forces and is deposited – A graded sequence of sedimentary rocks6-7Coarse-grained, typically gray colored rock composed of a mixture of different types of rocks and minerals
WackestoneMud-supported carbonate rock that contains greater than 10% grains

List of metamorphic rocks

Metamorphic RocksDescriptionMohr’s Hardness RatingDistinguishing Properties
AnthraciteHard, compact variety of coal2.5-3.5Shiny black, breaks with conchoidal fracture
AmphiboliteA metamorphic rock containing mainly amphibole and plagioclase6-7Class of high-grade medium to coarse-grained metamorphic rocks
BlueschistType of metavolcanic rock5-6Blue-green color, often with visible crystals
CataclasiteRock found at geological faults – A rock formed by faulting2.5-6Fragmented texture, formed by faulting
EclogiteA dense metamorphic rock formed under high pressure6.5-7.5Green and red coloration, often with visible crystals
GneissCommon high-grade metamorphic rock6-7Banded appearance, with alternating layers of different minerals
GranuliteType of foliated metamorphic rock – A low-grade metamorphic rock composed mostly of micaceous minerals7-8Coarse-grained, with visible crystals
GreenschistA mafic metamorphic rock dominated by green amphiboles5-6Green coloration, often with visible crystals
HornfelsSeries of contact metamorphic rocks that have been baked and indurated by the heat of intrusive igneous masses.6-7Fine-grained, often with a dull luster
CalcflintaA type of hornfels found in the Scottish HighlandsFine-grained, dark-colored rock
LitchfielditeNepheline syenite gneissLight-colored, with visible crystals
MarbleType of rock – a metamorphosed limestone3-4Light-colored, often with visible veins
MigmatiteMixture of metamorphic rock and igneous rockBanded appearance, with layers of different minerals
MyloniteA metamorphic rock formed by shearing4-6Fine-grained, often with a foliated texture
MetapeliteA metamorphic rock with a protolith of clay-rich (siltstone) sedimentary rockFine-grained, often with visible foliation
MetapsammiteA metamorphic rock with a protolith of quartz-rich (sandstone) sedimentary rockCoarse-grained, often with visible crystals
PhylliteMetamorphic rock – A low-grade metamorphic rock formed from shale or silts1-2Fine-grained, often with visible foliation
PseudotachyliteGlassy, or very fine-grained, rock type – A glass formed by melting within a fault via frictionDark-colored, glassy texture
QuartziteHard, non-foliated metamorphic rock which was originally pure quartz sandstone – A metamorphosed sandstone typically composed of >95% quartz7Shiny appearance, glassy surface, with few visible minerals
SchistEasily split medium-grained metamorphic rock3.5-4Foliated texture, visible minerals, medium to coarse-grained
SerpentiniteRock formed by hydration and metamorphic transformation of olivine2.5-4Dark green color, often with a scaly texture, can be easily carved
SkarnHard, coarse-grained, hydrothermally altered metamorphic rocks3.5-4Banded appearance, with alternating layers of different minerals, often with visible crystals
SlateA metamorphosed ultramafic rock with talc as an essential constituent, similar to a serpentinite2.5-4Fine-grained, often with visible foliation, splits into thin sheets
SueviteRock consisting partly of melted material formed during an impact event – A rock formed by partial melting during a meteorite impactBrecciated texture, with clasts of various sizes and shapes, often with melt veins
Talc carbonateA high-pressure metamorphic rock containing talc and kyanite
Soapstone – Talc-bearing metamorphic rock – Essentially a talc schistSoft texture, can be easily scratched with a fingernail, often with a soapy feel
TectoniteRock type – A rock whose fabric reflects the history of its deformationFoliated texture, visible minerals, medium to coarse-grained
WhiteschistA high pressure metamorphic rock containing talc and kyaniteWhite color, often with a banded appearance, visible minerals

List of Misc rock varieties

Igneous rocksDescriptionMohr’s Hardness RatingDistinguishing Properties
AdamelliteType of igneous rock – A variety of quartz monzonite5.5-6.5Light-colored, often with visible veins
AppiniteA group of varieties of lamprophyre, mostly rich in hornblende5-6Fine-grained, often with a dark color
AphaniteIgneous rock composed of very small crystals invisible to the naked eye5-6Uniform texture, often with a porphyritic structure
BorolaniteVariety of nepheline syenite from Loch Borralan, Scotland – A variety of nepheline syenite from Loch Borralan, Scotland5.5-6.5Coarse-grained, often with visible crystals
Blue GraniteVariety of monzonite, an igneous rock6-7Visible crystals, often with a blue-gray color
EpidositeHydrothermally altered epidote- and quartz-bearing rock2.5-3.5Green color, often with visible quartz veins
FelsiteVery fine-grained volcanic rock that sometimes contains larger crystals6-7Prone to weathering, often with a reddish color
FlintCryptocrystalline form of the mineral quartz7Conchoidal fracture, often used to make tools
GanisterHard, fine-grained quartzose sandstone, or orthoquartzite7High silica content, often used in refractories
GossanIntensely oxidized, weathered or decomposed rock4-5Reddish-brown color, often with visible iron oxides
HyaloclastiteVolcaniclastic accumulation or brecciaGlassy texture, formed by volcanic activity
IjoliteIgneous rock consisting essentially of nepheline and augite5-6Coarse-grained, often with visible crystals
JadeititeMetamorphic rock found in blueschist-grade metamorphic terranes6.5-7Green color, often with visible jadeite minerals
JasperoidA hematite-silica metasomatite analogous to a skarnReddish-brown color, often with visible hematite
KenyteType of igneous rock – A variety of phonolite, first found on Mount Kenya5-6Fine-grained, often with a porphyritic structure
Lapis lazuliMetamorphic rock containing lazurite, prized for its intense blue color – A rock composed of lazurite and other minerals5-5.5Blue color, often with visible veins
LarvikiteVariety of monzonite, an igneous rock6-7Visible crystals, often with a blue-gray color
LitchfielditeA metamorphosed nepheline syenite occurrence near Litchfield, MaineLight-colored, often with visible crystals
LlaniteType of mineral – A hypabyssal rhyolite with microcline and blue quartz phenocrysts from the Llano Uplift in TexasVisible blue quartz phenocrysts
LuxullianiteRare type of granite6-7Coarse-grained, often with visible crystals
MangeritePlutonic intrusive igneous rock, that is essentially a hypersthene-bearing monzonite6-7Light-colored, often with visible veins
MinetteA variety of lamprophyre5-6Fine-grained, often with a dark color
NovaculiteA type of chert found in Oklahoma, Arkansas, and Texas
PietersiteBreccia rock of hawk’s eyes and tiger’s eyes
PyroliteTheoretical rock making up the earth’s upper mantleLarge-grained crystals in a fine matrix, euhedral rhombic phenocrysts of feldspar
Rapakivi graniteType of igneous rock
Rhomb porphyryTextural form of igneous rock – A type of latite with rhombic phenocrysts of feldspar6-7Large grained crystals in a fine matrix, euhedral rhombic phenocrysts of feldspar
RodingiteMetamorphic rock – A mafic rock metasomatized by serpentinization fluids5-6Metasomatized by serpentinization fluids
ShonkiniteIntrusive igneous rock – melitilic and kalsititic rocks5-6Fine-grained, often with a porphyritic structure
TaconiteVariety of iron-bearing sedimentary rock
TachyliteForm of basaltic volcanic glass5.5-6Glassy texture
TescheniteA silica undersaturated, analcime bearing gabbroAnalcime bearing
TheraliteIgneous rock – A nepheline gabbro5-6
UnakiteMetamorphic rock – An altered granite
VarioliteIgneous rocks which contain variolesContains varioles
VogesiteUltrapotassic igneous rocks – A variety of lamprophyreCoarse-grained, often with visible crystals
WadPorous secondary manganese oxyhydroxide – A rock rich in manganese oxide or manganese hydroxideRich in manganese oxide or manganese hydroxide

Additional resources for rockhounds

Rock identification flowcharts

A rockhound can use flowcharts like the ones below to move through the rock-identification steps. Start with the boxes on the left and work your way to the right. You can use these charts when rockhounding to quickly identify a rock or rock type without conducting detailed tests.

  • Simplified rock identification and origin flowchart
  • Mineral identification flowchart
  • Rock identification flowchart

The most desirable (and valuable) rocks, minerals and gems by state

Below is a table of all 50 states and the most valuable rocks, minerals, and gems that are commonly found by rockhounds in each state.

StateRocks, Minerals, and Gems
AlabamaHematite, Quartz, Pyrite, Limestone, Marble, Barite, Coal
AlaskaGold, Quartz, Tourmaline, Garnets, Zinc, Lead, Silver, Platinum, Diamonds
ArizonaTurquoise, Copper, Amethyst, Garnets, Silver, Gold, Diamonds, Petrified Wood
ArkansasDiamonds, Quartz, Bauxite, Wavellite, Marcasite, Magnetite, Barite, Galena
CaliforniaGold, Jade, Serpentine, Tourmaline, Garnets, Topaz, Aquamarine, Benitoite
ColoradoRhodochrosite, Amazonite, Aquamarine, Fluorite, Topaz, Garnets, Quartz, Amethyst
ConnecticutGarnet, Beryl, Topaz, Danburite, Sulfides, Wollastonite, Staurolite
DelawareSillimanite, Zinc, Kaolin, Iron, Beryl, Talc, Feldspar
FloridaAgatized Coral, Calcite, Barite, Phosphate, Apatite, Celestine, Selenite
GeorgiaStaurolite, Kyanite, Quartz, Beryl, Galena, Pyrite, Limonite, Magnesite
HawaiiBlack Coral, Olivine, Quartz, Tourmaline, Jasper, Agate, Halite
IdahoStar Garnet, Opal, Jade, Gold, Silver, Galena, Pyrite, Sapphires
IllinoisFluorite, Galena, Calcite, Barite, Sphalerite, Celestine, Marcasite
IndianaCalcite, Selenite, Celestine, Pyrite, Dolomite, Quartz, Sphalerite
IowaGeodes, Calcite, Barite, Celestine, Pyrite, Sphalerite, Marcasite
KansasBarite, Calcite, Galena, Fluorite, Selenite, Celestine, Halite
KentuckyFluorite, Barite, Calcite, Galena, Sphalerite, Marcasite, Pyrite
LouisianaAgate, Limestone, Sulfur, Barite, Halite, Gypsum, Petroleum
MaineTourmaline, Beryl, Quartz, Mica, Feldspar, Gems, Pegmatites
MarylandAgate, Selenite, Chalcedony, Native Copper, Serpentine, Jasper, Staurolite
MassachusettsRhodonite, Babingtonite, Tourmaline, Beryl, Topaz, Mica, Feldspar
MichiganCopper, Agate, Greenstone, Datolite, Chlorastrolite, Calcite, Celestine
MinnesotaLake Superior Agate, Calcite, Thomsonite, Sphalerite, Galena, Pyrite, Quartz
MississippiMagnesite, Sphalerite, Barite, Fluorite, Calcite, Celestine, Galena
MissouriGalena, Calcite, Barite, Sphalerite, Marcasite, Pyrite, Celestine
MontanaSapphires, Garnet, Agate, Quartz, Gold, Silver, Copper, Platinum
NebraskaPrairie Agate, Calcite, Rhodochrosite, Chalcedony, Quartz, Selenite, Pyrite
NevadaTurquoise, Opal, Garnet, Silver, Gold, Copper, Lead, Barite
New HampshireSmoky Quartz, Beryl, Topaz, Tourmaline, Mica, Feldspar, Pegmatites
New JerseyFluorite, Magnetite, Zinc, Andradite Garnet, Prehnite, Pyrite, Franklinite
New MexicoTurquoise, Copper, Geodes, Agate, Fluorite, Calcite, Barite
New YorkGarnet, Herkimer Diamonds, Calcite, Celestine, Sphalerite, Galena, Dolomite
North CarolinaEmerald, Ruby, Sapphire, Aquamarine, Quartz, Feldspar, Mica, Spodumene
North DakotaPetrified Wood, Agate, Calcite, Gypsum, Selenite, Barite, Celestine
OhioFluorite, Celestine, Calcite, Sphalerite, Galena, Pyrite, Dolomite
OklahomaBarite, Quartz, Selenite, Galena, Calcite, Sphalerite, Pyrite
OregonSunstone, Opal, Jasper, Agate, Thundereggs, Zeolites, Obsidian
PennsylvaniaQuartz, Calcite, Pyrite, Sphalerite, Galena, Celestine, Geodes
Rhode IslandBowenite, Quartz, Pyrite, Selenite, Calcite, Garnet, Beryl
South CarolinaAmethyst, Beryl, Kyanite, Aquamarine, Quartz, Feldspar, Mica
South DakotaFairburn Agate, Rose Quartz, Petrified Wood, Calcite, Pyrite, Barite, Galena
TennesseeAgate, Fluorite, Calcite, Pyrite, Sphalerite, Galena, Barite
TexasTopaz, Fluorite, Geodes, Agate, Calcite, Selenite, Barite
UtahTopaz, Copper, Beryllium, Garnet, Agate, Fluorite, Calcite
VermontGrossular Garnet, Beryl, Quartz, Talc, Graphite, Garnet, Mica
VirginiaKyanite, Amazonite, Garnet, Pyrite, Sulfides, Staurolite, Epidote
WashingtonPetrified Wood, Agate, Jasper, Garnet, Topaz, Quartz, Pyrite
West VirginiaCoal, Cassiterite, Quartz, Celestine, Sphalerite, Galena, Pyrite
WisconsinGalena, Agate, Calcite, Sphalerite, Celestine, Pyrite, Marcasite
WyomingNephrite Jade, Jadeite, Agate, Sapphires, Garnet, Gold, Platinum

Image Credits

In-Article Image Credits

Rocky side of a mountain via Wikimedia Commons with usage type - GNU Free. August 23, 2006
Simplified rock identification and origin flowchart via Purdue University with usage type - Editorial use (Fair Use)
Mineral identification flowchart via Purdue University with usage type - Editorial use (Fair Use)
Rock identification flowchart via Purdue University with usage type - Editorial use (Fair Use)
Examples of Metamorphic rocks via American Museum of Science and History with usage type - Editorial use (Fair Use)
Examples of Sedimentary rocks via American Museum of Science and History with usage type - Editorial use (Fair Use)
Examples of igneous rocks via American Museum of Science and History with usage type - Editorial use (Fair Use)

Featured Image Credit

Rocky side of a mountain via Wikimedia Commons with usage type - GNU Free. August 23, 2006


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