Chart 1f - Gabbroic Rocks with Hornblende. IUGS classification of gabbroic rocks based on the relative modal proportions of pyroxene (Px), plagioclase (Pl), and Hornblende (Hbl). Some of the names depend on the relative modal proportions of orthopyroxene (Opx) and clinopyroxene (Cpx). Use the slider to select the Opx-Cpx proportions for the rock. If the rock has more than 5% modal quartz relative to feldspar, add "quartz" as a prefix to the name. If the rock has feldspathoid, add "foid-bearing" as a prefix to the name.