Classification of igneous rocks
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Transcript of Classification of igneous rocks
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Classification of igneous rocksClassification of igneous rocks
Phaneritic: Phaneritic: crystals visible with naked eyecrystals visible with naked eye
Plutonic Plutonic oror intrusive rocks intrusive rocks
Aphanitic: Aphanitic: crystal too small for naked eyecrystal too small for naked eye
Volcanic Volcanic oror extrusive rocks extrusive rocks
Phaneritic
Aphanitic
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Porphyritic: Porphyritic: two different, two different, dominant grain sizesdominant grain sizes
Large Crystals = Large Crystals = phenocrysts; Small Crystals Small Crystals = groundmass
Fragmental: Fragmental: composed of disagregated igneous material Pyroclastic rocks
Porphyritic
Pyroclastic
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Pegmatitic: Pegmatitic: very large xtals (cm to 10s of cm); i.e., very large xtals (cm to 10s of cm); i.e., slowlyslowly cooled cooledForms veins or layers within plutonic bodyForms veins or layers within plutonic body
Glassy: Glassy: non-crystalline; cools very fast (e.g., non-crystalline; cools very fast (e.g., obsidian)obsidian)Volcanic rocksVolcanic rocks
Vesicular:Vesicular: vesicles (holes, pores, cavities) form as vesicles (holes, pores, cavities) form as gases expandgases expandVolcanic rocksVolcanic rocks
Pegmatitic
Glassy
Vesicular
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Classification of Igneous RocksClassification of Igneous Rocks
Classification of the pyroclastic rocks. a. Based on type of material. After Pettijohn (1975) Sedimentary Rocks, Harper & Row, and Schmid (1981) Geology, 9, 40-43. b. Based on the size of the material. After Fisher (1966) Earth Sci. Rev., 1, 287-298.
Pyroclastic rocks
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Compositional terms for igneous rocksCompositional terms for igneous rocks
Felsic: Felsic: felfeldspar + dspar + sisilica lica
~55-70% silica, K-feldspar > 1/3 of feldspars present~55-70% silica, K-feldspar > 1/3 of feldspars present
light-colored silicate minerals — Continental crustlight-colored silicate minerals — Continental crust
Intermediate:Intermediate: between felsic and mafic between felsic and mafic
~55-65% silica, plag > 2/3 of feldspars present~55-65% silica, plag > 2/3 of feldspars present
Na-rich plag predominates over Ca-rich plagNa-rich plag predominates over Ca-rich plag
Mafic: Mafic: mamagnesium + gnesium + feferric ironrric iron
~45-50% silica; Ca-rich plag dominant feldspar~45-50% silica; Ca-rich plag dominant feldspar
dark silicate minerals — Oceanic crustdark silicate minerals — Oceanic crust
Ultramafic: Ultramafic: >90% mafic minerals, silica < 45%, few or no feldspars>90% mafic minerals, silica < 45%, few or no feldspars
Mantle-derivedMantle-derived
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Classification of common igneous rocksClassification of common igneous rocks
CompositionComposition PhaneriticPhaneritic AphaniticAphanitic Color indexColor index(% dark minerals)(% dark minerals)
FelsicFelsic GraniteSyeniteMonzonite
RhyoliteTrachyteLatite
101520
IntermediateIntermediate GranodioriteDiorite
Dacite Andesite
2025
MaficMafic Gabbro Basalt 50
UltramaficUltramafic Peridotite 95
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Mineralogical terms of Igneous RocksMineralogical terms of Igneous Rocks
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Mineralogical terms of Igneous RocksMineralogical terms of Igneous Rocks
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Classification of Igneous RocksClassification of Igneous Rocks
. A chemical classification of volcanics based on total alkalis vs. silica. After Le Bas et al. (1986) J. Petrol., 27, 745-750. Oxford University Press.
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Classification of Classification of Phaneritic Phaneritic
Igneous RocksIgneous Rocks
Figure. A classification of the phaneritic igneous rocks. a. Phaneritic rocks with more than 10% (quartz + feldspar + feldspathoids). After IUGS.
The rock must contain a total ofat least 10% of the minerals below.Renormalize to 100%
(a)
Quartz-richGranitoid
9090
6060
2020Alkali Fs.Quartz Syenite Quartz
SyeniteQuartz
MonzoniteQuartz
Monzodiorite
Syenite Monzonite Monzodiorite
(Foid)-bearingSyenite
5
10 35 65
(Foid)-bearingMonzonite
(Foid)-bearingMonzodiorite
90
Alkali Fs.Syenite
(Foid)-bearingAlkali Fs. Syenite
10
(Foid)Monzosyenite
(Foid) Syenite
(Foid)Monzodiorite
(Foi
d) G
abbr
o
Qtz. Diorite/Qtz. Gabbro
5
10
Diorite/Gabbro/Anorthosite
(Foid)-bearingDiorite/Gabbro
60
(Foid)olites
Quartzolite
Granite Grano-diorite
Tonalite
Alka
li Feld
spar
Gra
nite
Q
A P
F
60
Plutonic rocks
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Classification of Classification of AphaniticAphanitic
Igneous RocksIgneous Rocks
A classification and nomenclature of volcanic rocks. After IUGS.
(foid)-bearing Trachyte
(foid)-bearing Latite
(foid)-bearing Andesite/Basalt
(Foid)ites
10
60 60
35 65
10
20 20
60 60
F
A P
Q
Rhyolite Dacite
Trachyte Latite Andesite/Basalt
Phonolite Tephrite
Volcanic rocks
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Classification of Igneous RocksClassification of Igneous Rocks
Figure. A classification of the phaneritic igneous rocks. b. Gabbroic rocks. c. Ultramafic rocks. After IUGS.
Plagioclase
OlivinePyroxene
Olivine gabbro
Plagioclase-bearing ultramafic rocks
90
(b)
Anorthosite
OlivineOlivine
ClinopyroxeneClinopyroxeneOrthopyroxeneOrthopyroxene
LherzoliteLherzoliteH
arzb
urgi
te
Wehrlite
Websterite
OrthopyroxeniteOrthopyroxenite
ClinopyroxeniteClinopyroxenite
Olivine Websterite
PeridotitesPeridotites
PyroxenitesPyroxenites
90
40
10
10
DuniteDunite
(c)
Gabbroicrocks
Ultramaficrocks