Figure 1.
QAPM tetrahedron and QAP (quartz, alkali feldspar, plagioclase) triangle showing 500 random variations on a 30,30,30 granite. The shaded pyramid and quadrilateral are the International Union of Geological Sciences granite fields. Naming a rock “granite” only places it somewhere in the shaded pyramid, whereas calling it a 30,30,30 granite places it in the center of the QAP triangle and 10% off the base.