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Description: This rock is a course-grained igneous rock called a diorite. A diorite is an intrusive igneous rock of intermediate composition formed via the solidification of magma within the crust (i.e., within a magma chamber). The mineralogy of a diorite is dominated by amphibole, usually hornblende (black mineral), and plagioclase (white mineral). Notice the shape of the minerals within this rock: the black hornblende amphibole is well-shaped with straight edges while the white plagioclase seems to be filling in the spaces around the hornblende. This is an important observation as it indicates that the hornblende formed first, followed by the plagioclase filling in the spaces around the hornblende crystals. This rock also contains a granite xenolith (beige rock fragment), which represents a fragment of rock that broke off around the magma chamber and integrated itself into the magma as it was solidifying.