Classification of Igneous Rocks

1
Classification 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 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 of Igneous Rocks
(a)
Q
The rock must contain a total of
at least 10 of the minerals below.
Quartzolite
Renormalize to 100
90
90
Quartz-rich
Granitoid
60
60
Grano-
Tonalite
Granite
Alkali Feldspar Granite
diorite
Alkali Fs.
Qtz. Diorite/
20
20
Quartz Syenite
Qtz. Gabbro
Quartz
Quartz
Quartz
Monzonite
Syenite
Monzodiorite
Alkali Fs.
5
5
Diorite/Gabbro/
Syenite
Syenite
Monzonite
Monzodiorite
Anorthosite
35
90
10
65
A
P
(Foid)-bearing
(Foid)-bearing
(Foid)-bearing
Syenite
Monzonite
Monzodiorite
(Foid)-bearing
10
10
Diorite/Gabbro
(Foid)-bearing
Alkali Fs.
Syenite
(Foid)
(Foid) Syenite
(Foid)
Monzosyenite
Monzodiorite
(Foid) Gabbro
Figure 2-2. A classification of the phaneritic
igneous rocks. a. Phaneritic rocks with more than
10 (quartz feldspar feldspathoids). After
IUGS.
60
60
(Foid)olites
F
4
Classification of Igneous Rocks
Figure 2-2. A classification of the phaneritic
igneous rocks. b. Gabbroic rocks. c. Ultramafic
rocks. After IUGS.
(c)
5
Classification of Igneous Rocks
Figure 2-3. A classification and nomenclature of
volcanic rocks. After IUGS.
6
Classification 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 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.