Monzonite

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.[1] It may contain minor amounts of hornblende, biotite and other minerals. If quartz constitutes greater than 5%, the rock is termed a quartz monzonite.[2]

Monzonite
Igneous rock
Monzonite specimen from Rock Library (NASA JPL)
Composition
Mostly plagioclase and alkali feldspar
Not to be confused with the rare earth-bearing phosphate mineral Monazite.
Photomicrograph of thin section of monzonite (in cross polarised light)
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

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.[2]

Etymology

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.[1]

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See also

References
  1. Le Maitre, R.W., Igneous Rocks: A Classification and Glossary of Terms Cambridge University Press, 2nd ed, pp. 113 ISBN 0-521-66215-X
  2. 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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