Northern Black Mountains | Mohave County.
Dark-colored inclusions of fine-grained hornblende diorite contained within medium-grained biotite monzogranite of the Miocene-age Mount Perkins pluton. Many of the inclusions have sharp chilled margins, notably darker and finer-grained than the interiors. They are interpreted as having formed from mafic magma emplaced into granitic host magma that was only partially crystallized.
(Photo & caption by Brad Johnson, AZGS)
Photographer: Brad Johnson
Photo Date: March 2011