monzonite

Monzonite is an igneous intrusive rock, formed by slow cooling of underground magma that has a moderate silica content and is enriched in alkali metal oxides. Monzonite is composed mostly of plagioclase and alkali feldspar.

Syenodiorite is an obsolescent term for monzonite or for monzodiorite. Larvikite is a particular form of monzonite. ==Description== thumb|QAPF diagram for classification of intrusive igneous rocks, with the monzonite field highlighted thumb|Photomicrograph of [[thin section of monzonite (in cross polarised light)]] thumb|Photomicrograph of thin section of monzonite (in plane polarised light) thumb|The Notch Peak monzonite intrusion in [[Utah inter-fingers (partly as a dike) with highly metamorphosed Cambrian carbonate host rocks]] Monzonite is a coarse-grained (phaneritic) igneous rock. Such rocks are classified by their relative percentages of quartz, plagioclase, alkali feldspar, and feldspathoid (the QAPF classification). Monzonite is defined as rock having less than 5% quartz in its QAPF fraction and in which alkali feldspar makes up between 35% and 65% of the total feldspar content. If quartz constitutes greater than 5% of the QAPF fraction, the rock is termed a quartz monzonite, while if feldspathoids are present as up to 10% of the QAPF fraction, the rock is termed a feldspathoid-bearing monzonite. Rock richer in alkali feldspar is classified as syenite, while rock richer in plagioclase is termed a monzodiorite. The volcanic equivalent of monzonite is latite.