Monzonite

monzonite

Type of igneous rock that contains abundant and approximately equal amounts of plagioclase and potash feldspar, as well as other minerals. The type region is Monzoni, Italy, in the Italian Tirol; similar rocks have been described from Montana, Norway, Sakhalin Island, and other localities. Monzonite is not rare, but it generally occurs in rather small, heterogeneous masses mixed with diorites, pyroxenites, or gabbros.

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monzonite [′män·zə‚nīt]

(petrology)

A phaneritic (visibly crystalline) plutonic rock composed chiefly of sodic plagioclase and alkali feldspar, with subordinate amounts of dark-colored minerals, intermediate between syenite and dorite.

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Monzonite 

(named after the city of Monzoni, Italy, in the Tirol), crystalline igneous rock consisting of approximately equal amounts of common potash feldspar and lime-soda feldspar (orthoclase and labradorite) and of a ferromagnesian mineral, usually pyroxene. In more acid varieties of monzonite a small amount of quartz may also be present; in more basic kinds there may be olivine. Chemically the group of monzonite rocks occupies an intermediate position between gabbros and syenites (average silica content of 55–65 percent); therefore monzonites are also called gabbro-syenites. Monzonite is a dense large-grained rock that is attractive when polished. It is used as a building material. Monzonites occur in many regions of the USSR—for example, the Ukraine and the Baikal region; abroad they are found in Italy, Norway, and other countries.