Quartz monzonite is a felsic igneous rock that has an approximately equal proportion of orthoclase and plagioclase feldspars. The plagioclase is typically intermediate to sodic in composition, andesine to oligoclase. Quartz is present in significant amounts. Biotite and/or hornblende constitute the dark minerals. Quartz monzonite porphyry is often associated with copper mineralization in the porphyry copper ore deposits.
The granite in Joshua Tree National Park is composed primarily of quartz monzonite. It is a very abrasive granite as small sharp crystals within the rock do not wear down as quickly as the rock matrix it is embedded in. It is excellent for climbing as it has tremendous friction.
Quartz monzonite is also found in Black Canyon of the Gunnison National Park
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