Chart 2a. IUGS diagram for naming volcanic/aphanitic rocks with olivine < 10%. This QAPF diagram is two independent ternary diagrams that share the A-P edge. The upper triangle has the corners A-Q-P, where A is Alkali feldspar, Q is Quartz, and P is Plagioclase. The lower triangle has the corners A-P-F, where A is Alkali feldspar, P is Plagioclase, and F is Foid (meaning any feldspathoid mineral). Numbers on horizontal lines on the chart are ternary modal (=volume) percentage (Q relative to A+Q+P or F relative to A+P+F). Numbers on inclined or vertical lines are binary modal percentage (P relative to A+P).

For volcanic rocks with Olivine>10% click here: IUGS Volcanic QAPF
For only quartz-bearing volcanic/aphanitic rocks click here: IUGS Volcanic QAP
For only foid-bearing volcanic/aphanitic rocks click here: IUGS Volcanic FAP