Quartz-feldspar mylonite derived from granite, Santa Catalina Mountains, Tucson, Arizona


There is a mountain of this rock in the foothills of the Catalina Mountains, just a ‘stones throw’ from where I live.  I collected this rock in the mid-1970s while mapping and analyzing rocks and structures in the Catalinas and Rincons.  This rock ‘takes me back’ to all of the original confusion regarding naming this rock and interpreting its tectonic significance.  

Age & Formation
Original granite of Mesoproterozoic age, ~1.4 Ga. Age of mylonitization, ~25-18 Ma.