PLAGIOCLASE - 50-100%
Orthoclase - 10-35%
Mafics - < 10%
Quartz - 0-5%
Monzonite is one of three rocks dominated by feldspar (the others being anorthosite and syenite) with occasional other minerals thrown in in lesser amounts (although the rock can go 100% plagioclase.) The plagioclase is sodium rich, unlike anorthosite which is calcium rich.
Because monzonite is light colored it is often confused with granite but granite has quartz >20%. Monzonites with quartz 5-20% are "quartz monzonites." Less than 5% quartz and the rock is just monzonite
Monzonite is not a common rock, but is typically found around the edges of other felsic plutons, such as plagiogranites or granodiorites. That is, it is typical of continents.