Introductory Igneous Rock Classifications usually establish four megascopic equigranular families based on mineral composition

Introductory Igneous Rock Classifications usually establish four megascopic equigranular families based on mineral composition. These mineral combinations form the four Igneous Rock Families. Critical thinking question: Why should some minerals crystallize together to form the same type of rock?

Rock Family	Essential Minerals	Position on Y
Granite	Quartz and Orthoclase	Lower Stem of Y
Diorite	Albite and Hornblende	Mid Junction of Y
Gabbro	Anorthite and Hornblende	Diagonally Across Y
Peridoite	Olivine and Augite	Upper Left Arm of Y