Geology Reference
In-Depth Information
Q
Quartz-rich
rocks
60
60
Grano-
diorite
Granite
10
65
90
20
Gabbro,
diorite and
anorthosite
Syenite
A
P
50
Foid
Syenite
Foid diorite
and gabbro
60
60
Foid-rich
rocks
F
Figure 3.11
Simplified QAPF diagram for naming medium- and coarse-grained
rocks in the field using their salic mineral content (see text and appendix
Figure A.1 for further details). Most igneous rocks fall in the shaded area.
Remember that foid is an abbreviation for feldspathoid.
less than 90%, primarily using the relative proportions of their different felsic
minerals: Q
=
quartz, A
=
alkali feldspars, P
=
plagioclase feldspars, F
=
feldspathoid minerals (e.g. nepheline and leucite in Table 3.4, though there
are other feldspathoids; these minerals have similar chemistry to feldspars
but with less SiO
2
and are often collectively known by the abbreviation foid
minerals). Figure 3.11 is a simplified version of the QAPF diagram which,
