The document discusses different classification schemes for igneous rocks. It provides figures that classify igneous rocks based on their mineralogical composition and textures. Figure 2-1 shows how to plot mineral components on ternary diagrams. Figures 2-2 and 2-3 classify phaneritic, gabbroic, ultramafic, and volcanic rocks based on their mineralogy. Figure 2-4 classifies volcanic rocks based on their total alkalis and silica content. Figure 2-5 classifies pyroclastic rocks based on material type and size of fragments.

1. Classification of Igneous RocksClassification of Igneous Rocks
Figure 2-1a. Method #1 for plotting a point with the components: 70% X, 20% Y, and 10% Z on
triangular diagrams. An Introduction to Igneous and Metamorphic Petrology, John Winter, Prentice Hall.

2. Classification of Igneous RocksClassification of Igneous Rocks
Figure 2-1b. Method #2 for plotting a point with the components: 70% X, 20% Y, and 10% Z on triangular
diagrams. An Introduction to Igneous and Metamorphic Petrology, John Winter, Prentice Hall.

3. Classification ofClassification of
Igneous RocksIgneous Rocks
Figure 2-2. 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 of
at least 10% of the minerals below.
Renormalize to 100%
(a)
Quartz-rich
Granitoid
9090
6060
2020Alkali Fs.
Quartz Syenite
Quartz
Syenite
Quartz
Monzonite
Quartz
Monzodiorite
Syenite Monzonite Monzodiorite
(Foid)-bearing
Syenite
5
10 35 65
(Foid)-bearing
Monzonite
(Foid)-bearing
Monzodiorite
90
Alkali Fs.
Syenite
(Foid)-bearing
Alkali Fs. Syenite
10
(Foid)
Monzosyenite
(Foid)Syenite
(Foid)
Monzodiorite
(Foid)Gabbro
Qtz. Diorite/
Qtz. Gabbro
5
10
Diorite/Gabbro/
Anorthosite
(Foid)-bearing
Diorite/Gabbro
60
(Foid)olites
Quartzolite
Granite Grano-
diorite
Tonalite
AlkaliFeldsparGranite
Q
A P
F
60

4. Classification of Igneous RocksClassification of Igneous Rocks
Figure 2-2. A classification of the phaneritic
igneous rocks. b. Gabbroic rocks. c. Ultramafic
rocks. After IUGS.
Plagioclase
OlivinePyroxene
Gabbro
Troctolite
Olivine
gabbro
Plagioclase-bearing ultramafic rocks
90
(b)
Anorthosite
OlivineOlivine
ClinopyroxeneClinopyroxeneOrthopyroxeneOrthopyroxene
LherzoliteLherzolite
Harzburgite
WehrliteWebsterite
OrthopyroxeniteOrthopyroxenite
ClinopyroxeniteClinopyroxenite
Olivine Websterite
PeridotitesPeridotites
PyroxenitesPyroxenites
90
40
10
10
DuniteDunite
(c)

5. Classification ofClassification of
Igneous RocksIgneous Rocks
Figure 2-3. 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

6. Classification of Igneous RocksClassification of Igneous Rocks
Figure 2-4. 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.

7. Classification of Igneous RocksClassification of Igneous Rocks
Figure 2-5. 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.