Figure 1.05. Basalt tetrahedron. Basalt classification based on normative mineralogy proposed by Yoder and Tilley (1962) and expanded to include iron and anorthite (An) by Morse (1980, p.16). Tholeiites are basalts that have quartz (Qz) in the norm. Basalts that have both quartz and olivine (Ol) are are olivine tholeiites. Basalts that have nepheline (Ne) instead of quartz in the norm are alkali basalts. Other mineral abbreviations used are for clinopyroxene (Cpx), orthopyroxene (Opx), and plagioclase (Pl) for the the Fe + anorhtite included diagrams, and forsterite (Fo), enstatite (En), and albite (Ab) for the end-menber version. You may use your mouse wheel and mouse to zoom and pan the image to see more detail. Press the "Recenter" button to return to the original view.