Phoenix Mountains, Phoenix, Arizona | Steve Reynolds, Arizona State University professor, describing Proterozoic-age phyllites – a fine-grained metamorphic rock – exposed in the Phoenix Mountains, north Phoenix, to geologists participating in the fall 2012 Arizona Geological Society field trip. Note the slatey cleavage of the rock outcrop and the small, flagstone-size pieces of rock debris at Steve’s feet. The phyllites are exposed near Dreamy Draw, aptly named for the impact that mining of a cinnabar (mercury-bearing mineral) deposit had on miners.
For a geologic map and report see the “Geologic Map of the Phoenix Mountains, Central Arizona” by Steve Reynolds and D.A. Jones at the AZGS Document Repository. http://repository.azgs.az.gov/uri_gin/azgs/dlio/1110