classification of igneous rocks
DESCRIPTION
Classification of Igneous rocksTRANSCRIPT
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
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
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
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
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
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
Mineralogical terms of Igneous RocksMineralogical terms of Igneous Rocks
Mineralogical terms of Igneous RocksMineralogical terms of Igneous Rocks
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.
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
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
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