Monzonite

Not to be confused with the rare earth-bearing phosphate mineral Monazite.

Photomicrograph of thin section of monzonite (in cross polarised light)

The QAPF diagram, by which a monzonite is defined

Photomicrograph of thin section of monzonite (in plane polarised light)

An intrusion (Notch Peak monzonite) inter-fingers (partly as a dike) with highly-metamorphosed host rock (Cambrian carbonate rocks). From near Notch Peak, House Range, Utah.

Monzonite is an intermediate igneous intrusive rock composed of approximately equal amounts of sodic to intermediate plagioclase and orthoclase feldspars with minor amounts of hornblende, biotite and other minerals. Quartz a minor constituent or is absent; with greater than 5% quartz the rock is termed a quartz monzonite.

If the rock has more orthoclase or potassium feldspar it grades into a syenite. With an increase of calcic plagioclase and mafic minerals the rock type becomes a diorite. The volcanic equivalent is the latite.

See also

• QAPF diagram