Monzonite is an igneous intrusive rock. It is composed of approximately equal amounts of plagioclase and alkali feldspar, with less than 5% quartz by weight. It may contain minor amounts of hornblende, biotite and other minerals. If quartz constitutes greater than 5%, the rock is termed a quartz monzonite.
If the rock has a greater percentage of alkali feldspar, it grades into a syenite. With an increase in calcic plagioclase and mafic minerals the rock type becomes a diorite. The volcanic equivalent is the latite.
Monzonite was originally named after the Monzoni range in Val di Fassa (Trento Province - Italy) where it is abundant. As rock definitions have been systematized and codified, this association has lost any relevance to the rock's definition.
- Le Maitre, R.W., Igneous Rocks: A Classification and Glossary of Terms Cambridge University Press, 2nd ed, pp. 113 ISBM 0-521-66215
- Klein, Cornelis and Cornelius S. Hurlbut, Jr., Manual of Mineralogy, Wiley, 20th ed, pp. 480-484 ISBN 0-471-80580-7
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