ABSTRACT
An ideal classification of magmas and magmatic rocks would group magmatic materials in an order that directs attention to petrogenetic relationships between individual rocks and magmas, and also between larger comagmatic groups. Rocks are essential because they provide the raw materials used in constructing the buildings, transport systems and artifacts of an industrialised society. To understand the implications of the decision by the Subcommission on the Systematics of Igneous Rocks to use modal data in their primary classificatíon, one has to recognise that there are many difficulties inherent in carrying out petrographic modal analyses. Heteromorphism is essentially what sets the charnockitic rock series apart from normal plutonic rocks. Textures describe the general physical appearance or character of a rock. Cumulates are magmatic rocks formed by the accumulation of crystals within a magma. Iron is an essential chemical component of the common magmas and igneous rocks.
