Discover The Wonders of Our Earth and the forces and life forms that shape our world with the Physical Geography Series. The third classification of rocks are those which were formed deep in the earth's crust by melting and then recrystallization. These rocks include volcanic rocks, igneous rocks of dykes and sills and plutonic rocks such as granite, syenite, gabbro and ultramafic rocks. Many specimens are discussed that are not often found in classroom labs or textbooks. Subjects covered include: Where igneous rocks come from, How igneous rocks are classified, Where igneous rocks can be found, Volcanic rocks, Ejected materials from volcanoes including ash and tuff.