Geology: Igneous Rocks Identification Chart, Study notes of Geology

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RIOCKDENTIFICATIONG & MUIDEINERAL

RIOCKDENTIFICATIONG & MUIDEINERAL

M INERALS

Igneous RockAphanitic -- Porphyritic -- Phenocrysts areolivine and pyroxene (therefore mafic)Olivine Pyroxene Basalt Porphyry

Igneous RockAphanitic -- Porphyritic -- Phenocrysts arePlagioclase Feldspar (therefore mafic)Plagioclase Feldspar Basalt Porphyry

Sedimentary Rocks. 57 Arkose .................... 63, 64Breccia .......................... 68Calcarenite .................... 77Chalk ............................. 76Chert ....................... 69, 70Conglomerate ......... 66, 67^ Index

Coquina ........................ 78Crystalline Limestone ... 73Diatomite ...................... 79Evaporitic Limestone .... 74Flint .............................. 71Graywacke .................... 65Limestone ..................... 72Mudstone ................ 58, 59Oolitic Limestone ......... 75Quartz Sandstone .... 61, 62 Shale ............................. 60

Metamorphic Blueschist ..................... 90Eclogite ......................... 96Gneiss ..................... 92, 93Greenschist ................... 91Greenstone .................... 95Hornfels ........................ 83Marble ........................... 82Migmatite ...................... 94 Rocks .................. 81 Phyllite .......................... 95Quartzite ....................... 98Schist ............................ 89Serpentinite ................... 97Skarn ................. 84, 85, 86Slate .............................. 87

Mineral (Silicate -- Sheet -- Mica)Not metallic -- 1 flexible cleavage plane (sheet),dark colored; brown streak.Biotite

Igneous RockFrothy -- Light colored (therefore felsic orintermediate)Pumice

Igneous RockAphanitic -- Porphyritic -- Phenocrysts areHornblende (therefore Intermediate)Hornblende Andesite Porphyry 50

Texture^ Name^ Parent rock^ GeologicGrade^ Descriptionsettings Foliated^ Slate^ Shale^ B, R, S^ Low^ Dull; similar to shale, but more dense and breaks into hard flat sheets. Novisible crystals. Phyllite Shale B, R, S^ Low-med^ Similar to slate, but sheets are undulating (wrinkled). Luster is more silky orsatiny than slate. Some isolated crystals might be visible. Schist Basalt/gabbro,B, R, S^ Med-high^ Crystals easily visible throughout rock – usually all micas, giving it a scalyshalelook. Foliation greater than phyllite. Minerals can be garnet + biotite + chlorite+ muscovite + quartz + plagioclase + epidote + kyanite. Chlorite disappearsand kyanite appears as grade increases. Blueschists contain a blue amphibole (glaucophane) or blue silicate similar to epidote (lawsonite). Formed through medium gradesubduction of basalt/gabbro. Greenschists^ contain green minerals (actinolite + epidote +/- chlorite) giving it a green appearance. Formedthrough medium grade burial of basalt/gabbro. (Can also contain hornblende + plagioclase +/- garnet.) Gneiss Granite/rhyolite,B, R, S^ High^ Grains medium to coarse; light and dark minerals segregated into bands.shaleGneissic texture. Migmatite Gneiss B, R, S^ Very high^ Contorted layers: gneissic texture that has been folded: some of thelayers/bands have melted and crystallized as granite. WeaklyGreenstone^ Basalt/gabbro^ foliated B, R, S^ Low^ Very fine grained (too small to see crystals); light to yellow green (fromchlorite, epidote, and/or actinolite). Eclogite Basalt/gabbro S^ High^ Red garnets scattered uniformly throughout a finer-grained green groundmass(bright-green pyroxene: omphacite). May have quartz, kyanite, or biotite. Serpentinite Peridotite H^ Med-high^ Green, mottled, massive. Smooth, rounded slippery surfaces. Can be black orreddish. Usually displays slickensides Soapstone Serpentinite S^ High^ White to green. Very soft. Soapy feel. Primary mineral is talc: can be scratchedwith fingernail. NonHornfels^ Basalt/gabbro, foliated mudstone Metamorphic Rock Identification Chart C^ All^ Sugary or microcrystalline, usually dark-colored. Marble^ Pure limestoneB, R, S, C^ All^ Sugary, sandy, or crystalline; calcite or dolomite (form of calcite with Mg) (CaCO) 3 (only CaCO^3 )crystals fused together. White to pink. Might have dark streaks. Quartzite^ Chert (only SiO^2 )B, R, S, C^ All^ Sugary, sandy, or crystalline; can sometimes see quartz sand grains fused (SiO) Quartz Sandstonetogether; grains won’t rub off like sandstone. (^2) Skarn Impure limestoneC^ All^ Crystalline; usually with large crystals, including calcite, quartz, garnet,or chert, arkose,epidote, pyroxene and other crystals, like sulfides.greywacke…

Mineral (Carbonate)Not metallic -- Bubbles in HCL. Doublerefraction (2 images visible through clearsample). Rhombs, 3 cleavage planes (not 90),H=3.Calcite CaCO 3 Igneous RockAphanitic -- Vesicular (<50%) -- Light Greycolor (therefore Intermediate)Andesite 49

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Chemical sedimentary rock^ (precipitated minerals or recrystallized shells – interlocking microscopic crystalline texture)^ Composition^ Texture and physical properties

Name^ Depositional environment Calcium carbonate^ Interlocking texture, crystals too fine to CaCO^3 see. Light brown, grey, or white.

Limestone Precipitation in the deep sea or recrystallization of shells (Dolostone if has Mg)accumulated on the deep sea floor (clastic texture gone).Spherical grains like tiny beads (<2 mm) Oolitic^ limestone^ Precipitation in the surf zone near reefs, around fine sandwith concentric laminations.grains, like oystersLayers of crystals – formed from Evaporitic or^ Precipitation in salt lakes and inland seas.evaporation of water. crystalline^ limestone Quartz SiO^2 Interlocking texture, crystals too fine tosee. White, red, brown, black, or green.

Chert^ Precipitation in the deep sea or hydrothermal zones orrecrystallization of shells accumulated on the deep seafloor (clastic texture gone).Black nodules, with powdery white rind. Flint^ (nodular chert)^ Precipitation in hydrothermal zones. Halite NaCl^ Crystalline; salty taste^

Rock salt^ Precipitation in salt lakes and inland seas. Gypsum CaSO^4 2H^2 O^ Very soft, crystalline^

Rock Gypsum^ Precipitation in salt lakes and inland seas. Clastic sedimentary rock^ (cemented or compacted clasts)^ Organic (biochemical) sedimentary rock^ (clasts are mostly shells)

Grain sizes:^ Gravel (>2mm); Sand (>1/16 mm; < 2 mm); Mud (<1/16) mm Composition and Texture^

Grain size^ Name^ Depositional environment Calcium carbonate CaCO^3

Gravel^ Coquina^ (limestone)^ Beach with fringing reef WHITE (usually); Macro/microscopic shell^

Sand^ Calcarenite^ (limestone)^ At outside edges of fringing reefs fragments; Loosely cemented; porous.^

Mud^ Chalk^ (limestone)^ Deep seafloor where plankton with microscopicCaCO^3 shells rain down. Silica SiO WHITE (usually); Macro/microscopic^2 shell fragments. Loosely cemented; porous.

Mud^ Diatomite^ (chert)^ Deep seafloor where plankton with microscopicSiO^2 shells rain down. Detrital sedimentary rock^ (clasts are mostly rock and/or mineral fragments^ Grain size^ Texture and composition^

Name^ Depositional environment Gravel^ Rounded fragments; poorly sorted Conglomerate^ Beach headlands, natural levees, tops of alluvialfans.

2 mm^ Angular fragments; poorly sorted^

Breccia^ Base of landslides, faults, and debris flows. Sand^ Mostly quartz grains; well sorted; well rounded

Quartz^ sandstone^ Beach, sand dunes (desert or beach); river banks.Source rock probably far away. < 2 mm^ >25% potassium feldspar grains, with quartz

Arkose^ Beach sands; river deposits. Source rock mostlikely feldspar-rich granite.

1/16 mm^ Mixed mineral grains/rock fragments.

Graywacke^ Beach sands; river deposits. Source rockprobably nearby. MudMicroscopic quartz/clay grains; can be bedded.< 1/16 mmShale variety is compact; splits into thin layers Sedimentary Rock Identification Chart^ Mudstone^ or^ Shallow, quiet lagoon; tide flats; outer^ Shale continental shelf; deep sea.

Mineral (Carbonate)Not metallic -- Bubbles in HCL. Doublerefraction (2 images visible through clearsample). Rhombs, 3 cleavage planes (not 90),H=3.Calcite CaCO (^3)

Sedimentary RockDetrital Clastic -- Mud-sized grains --NOT white -- doesn't break in layersMudstone

Igneous RockAphanitic -- Porphyritic -- Phenocrysts areK-Feldspar and Quartz (therefore Felsic)K-Feldspar & Quartz Rhyolite Porphyry

To identify (name) igneous rocks, you determine two things about the rock: composition and texture. First determine composition, which is basedon mineral content or color, if you can’t see minerals. Then determine the texture of the rock and based on the two, identify the rock name.

Composition Quartz^ PotassiumMuscovite^ Biotite^ Feldspar

Hornblende^ Plagioclase^ Pyroxene^ Olivine

Color index (if can’tCompositionalsee minerals)name 0 0 0 0

0 0-20%^ 0-20%^ 50-100%

Very dark^ Ultramafic 0 0 0 0

0-10%^ 20-60%^ 25-30%^ 0-50%

Dark^ Mafic 0 0 0 0-5%^

10-20%^ 10-60%^ 0-10%^0

Grey (medium dark)^ Intermediate 10-30%^ 0-50%^ 0-5%^ 0-5%^

0-10%^ 10%^0

Very light to salt and^ Felsic pepper colored (cancontain a lot of pink) Texture Phaneritic^ Aphanitic^

Glassy^ Frothy^

Pyroclastic 100% visible crystals^ Most crystals too small to see

100% glass^ Greater than 50% vesicles(rest is usually glass-like)

Fragments of ash,crystals, pumice, rocks Ultramafic^ Peridotite Mafic^ Gabbro^

Basalt^ Scoria

Volcanic Tuff Intermediate^ Diorite^

Andesite^ Pumice^ Volcanic Tuff Felsic^ Granite^

Rhyolite^ Obsidian^ Pumice

Volcanic Tuff Pegmatitic texture is aPorphyritic texture is asubcategory of Phaneriticsubcategory of Aphanitic(see below for naming(see below for naminginformation)information) Add PEGMATITE to the name IF the rock displays pegmatitic texture:

If an intrusive igneous rock has extremely large minerals (> 2 inches long), the rock is called a^ pegmatite. (Naming examples: granite pegmatite)

NOTE : All pegmatites are phaneritic rocks. Add PORPHYRY to the name IF the rock displays porphyritic texture.

If an aphanitic igneous rock has^ phenocrysts^ in it (large minerals surrounded by an aphanitic matrix), it is called

porphyritic. Add the name of the prominent phenocryst mineral to the front of the rock name. (Naming example: olivine basalt porphyry)^ NOTE

: All porphyries are aphanitic rocks, because the majority of the rock (the groundmass, or Igneous Rock Identification Chart matrix) is aphanitic.

Mineral (Halide)Not metallic -- Cubic or octahedral form.4 directions of cleavage.Fluorite

Sedimentary RockDetrital Clastic -- Mud-sized grains --NOT white -- doesn't break in layersMudstone

Igneous RockPhaneritic -- Olivine & pyroxene(therefore Ultramafic)Peridotite

Metamorphic RockNot foliated -- 100% Quartz (no reaction withacid)Parent rock: Chert (including Flint andDiatomite), Quartz SandstoneSetting: Low to High grade BRSCQuartzite

Mineral (Silicate)Not metallic -- Mottled green color. Smooth,curved surfaces. No cleavage. H>2.Serpentine

Sedimentary RockDetrital Clastic -- Sand-sized grains --Grains are mostly quartzQuartz Sandstone

Igneous RockPhaneritic -- Olivine (therefore Ultramafic)Peridotite

Metamorphic RockWeakly foliated -- Actinolite background withscattered garnets and kyaniteParent rock: Basalt -- Setting: High grade SEclogite

Mineral (Silicate -- Double Chain -- Amphibole)Not metallic -- H=5.5. Dark green or black.2 cleavages at 60 & 120. Splintery fracture.Long prisms.Hornblende

Sedimentary RockDetrital Clastic -- Sand-sized grains --Grains are mostly quartzQuartz Sandstone

Igneous RockPhaneritic -- Plagioclase Feldspar, Pyroxene(therefore Mafic)Gabbro

Metamorphic RockWeakly or not foliated -- Crystals too small tosee -- Green colored -- DullParent rock: BasaltSetting: Low grade BRSGreenstone

Mineral (Silicate -- Framework)Not metallic -- Subparallel exsolution lamellae.2 cleavages at 90. Pink or white color. H = 6.No twinning.Potassium Feldspar (K-Feldspar)

Sedimentary RockDetrital Clastic -- Sand-sized grains -- Grainscontain a significant amount of K-FeldsparArkose

Igneous RockPhaneritic -- Plagioclase Feldspar, Pyroxene(therefore Mafic)Gabbro

Metamorphic RockFoliation: Gneissic TextureParent rock: Shale/Mudstone (via Slate andPhyllite and Schist) OR GraniteSetting: High grade BRSGneiss

Mineral (Silicate -- Framework)Not metallic -- Twinning. 2 cleavages at 90.H = 6.Plagioclase Feldspar

Sedimentary RockDetrital Clastic -- Sand-sized grains --Grains are mostly rock fragmentsGraywacke

Igneous RockPhaneritic -- Plagioclase Feldspar, Hornblende,Biotite (therefore Intermediate)Diorite

Metamorphic RockFoliation: Gneissic TextureParent rock: Shale/Mudstone (via Slate andPhyllite and Schist) OR GraniteSetting: High grade BRSGneiss

Mineral (Native Element)Metallic -- H=1. Greasy. Dark grey streak.Graphite

Sedimentary RockDetrital Clastic -- Gravel-sized, rounded grains -Grains are a mixture of rock fragments andmineralsConglomerate

Igneous RockPhaneritic -- K-Feldspar, Quartz, Biotite,Muscovite, Hornblende (therefore felsic)Granite

Metamorphic RockFoliation: Schistose -- 100% visible crystals --Blue (Glauophane)Parent rock: Basalt (via Greenstone)Setting: Med grade SBlueschist

Mineral (Silicate)Not metallic -- Blue, flexible blades.Kyanite

Sedimentary RockDetrital Clastic -- Gravel-sized, angular grains --Grains are a mixture of rock fragments andmineralsBreccia

Igneous RockPhaneritic -- Quartz, K-Feldspar, Muscovite,Biotite (therefore Felsic)Granite

Metamorphic RockFoliation: Schistose -- 100% visible crystals --MicasParent rock: Shale/Mudstone (via Slate andPhyllite)Setting: Med grade BRSSchist

Mineral (Silicate -- Framework)Not metallic -- Glassy, conchoidal fracture, H=7.Hex. prism with pointed end.Quartz SiO 4

Sedimentary RockChemical -- 100% Quartz composition(doesn't react with acid)Chert

Igneous RockPyroclasticVolcanic Tuff

Metamorphic RockFoliation: Slaty Cleavage -- No visible crystalsParent rock: Shale/MudstoneSetting: Low grade BRSSlate

Mineral (Silicate -- Framework)Not metallic -- Glassy, conchoidal fracture, H=7.Hex. prism with pointed end.Quartz SiO 4

Sedimentary RockChemical -- 100% Quartz composition(doesn't react with acid) -- Black inside --Coating of Chalk on outsideFlint

Igneous RockFrothy -- Dark colored (therefore mafic)Scoria

Metamorphic RockNot foliated -- Calcite, Garnet, WollastoniteParent rock: Mudstone, Sandstone,Conglomerate, Breccia (as long as containsmixture of minerals)Setting: Low to High grade CSkarn