Quartz monzonite bedrock from a USGS drill core at Western Cape Cod, Massachusetts
Quartz monzonite (or adamellite) is an intrusive, felsic, igneous rock that has an approximately equal proportion of orthoclase and plagioclase feldspars. It is typically a light colored phaneritic (coarse-grained) to porphyritic granitic rock. 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. Because of its coloring, it is often confused with granite, but whereas granite contains more than 20% quartz, quartz monzonite is only 5–20% quartz. Rock with less than five percent quartz is classified as monzonite. A rock with more alkali feldspar is a syenite whereas one with more plagioclase is a quartz diorite. The fine grained volcanic rock equivalent of quartz monzonite is quartz latite.
Quartz monzonite extracted from a quarry in Little Cottonwood Canyon was used to build several buildings in Salt Lake City, Utah, including the LDS Church's Salt Lake Temple, the Utah State Capitol, the LDS Church Administration Building, and the facade of the nearby LDS Conference Center.
The large boulders of Joshua Tree National Park in southern California are quartz monzonite.
A large pluton in the Atlanta lobe of the Idaho Batholith, near McCall, Idaho, is made of quartz monzonite.
- Media related to Quartz monzonite at Wikimedia Commons
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