Definition of qapfm classification

The IUGS proposed a now generally accepted scheme for classifying igneous rocks by their mineral composition (modal composition).
The classification is based on 5 groups of minerals, which are either felsic or mafic:

felsic
Q Quartz
A Alkali-Feldspars
P Plagioclase Feldspars
F Foids (short for Feldspathoids)

mafic
M Mafic Minerals

Within the QAPFM classification any mineral that is not felsic is considered mafic.
Rocks with less than 90 vol-% mafic minerals are classified by their content of Q, A, P, and F.
Rocks that contain more than 90 vol-% mafic minerals are called ultramafic and classified in an independent scheme.

The IUGS recommends the QAPFM classification whenever the mineral composition of a rock can be determined (as opposed to the chemical composition). This can be difficult for volcanic and hypabyssal rocks, for which alternative classification schemes exist.

For an overview of the primary rock names and their definition, see
QAPF Diagram

Ultramafic Rocks