Chemical Clasification of Volcanic Rocks IUGS Modal Clasification of Igneous Rocks Q using TAS (total Alkali-Silica Diagram) after le Bas et al., 1986 Plutonic & Volcanic Q 90 90 14 phonolite Rocks M < 90% quartzolite Volcanic tephri- trachyte 12 phonolite 90 90 (q < 20%) Plutonic Gabbro / diorite foidite trachydacite Gabbro if An% > 50 or M> 35 10 phono- (q > 20%) 60 60 trachy- quartz-rich Pyroxene (not amphibole) tephrite granitoid andesite rhyolite SiO2 < 52% 8 tephrite O wt % 2 basaltic (ol<10%) 60 60 trachy- rhyolite dacite basanite andesite O + K (ol>10%) 2 6 trachy- granodiorite granite tonalite Na basalt dacite alkali feldspar rhyolite 10 35 65 90 quartz alkali 20 20 4 basaltic andesite feldspar trachyte quartz quartz basalt andesite quartz diorite basalt alkali feldspar granite trachyte latite quartz gabbro alkali feldspar andesite 2 picro- quartz alkali 10 35 65 90 quartz anorthosite 5 5 basalt 20 20 trachyte trachyte latite feldspar syenite quartz quartz qtz monzo monzodiorite A foid-bearing foid-bearing foid-bearing P syenite monzonite diorite / gabbro monzogabbro trachyte latite basalt / andesite 0 alkali feldspar Ultrabasic Basic Intermediate Silicic or Acid 5 5 foid-bearing 10 10 syenite syenite monzonite 10 50 90 diorite gabbro alkali feldspar 40 50 60 70 80 A foid-bearing foid-bearing P phonolitic basanite anorthosite trachyte phonolite syenite monzonite (olivine > 10%) SiO2 wt % tephritic foid-bearing 10 10 10 50 90 foid-bearing phonolite phonolitic tephrite alkali feldspar diorite / gabbro (olivine < 10%) syenite foid syenite foid basanite (olivine > 10%) monzodiorite tephrite (olivine < 10%) foid foid monzodiorite / gabbro monzosyenite foid monzogabbro Basalt / Andesite 60 60 foid diorite / gabbro Basalt if An% > 50 or M> 35 phonolitic tephritic foidite foidite Pyroxene (not amphibole) SiO2 < 52% 60 60 foidolite foidite Ultramafic Rocks M > 90% F Gabbroic Rocks Plag Plag Ol Ol anorthosite anorthosite dunite dunite F ANORTHOSITES 90 90 90 90 90 90 90 90 troctolite (LEUCO-) hornblende PERIDOTITE pyroxene wehrlite peridotite peridotite 65 65 65 65 pyroxene gabbro gabbro hornblende hornblende gabbronorite olivine gabbro gabbronorite gabbro harzburgite lherzolite peridotite norite olivine gabbronorite GABBROIDS norite olivine norite pyroxene hornblende 40 40 40 40 olivine gabbro/gabbronorite/norite olivine olivine olivine 35 35 35 35 hornblendite orthopyroxenite clinopyroxenite pyroxenite olivine olivine PYROXENITE & (MELA-) olivine websterite hornblende pyroxene HORNBLENDITE pyroxenite hornblendite 10 10 10 10 10 10 10 10 plagioclase-bearing plagioclase-bearing plagioclase-bearing ultramafic rocks ULTRAMAFIC ROCKS Opx websterite Cpx Px hornblende pyroxenite pyroxene hornblendite Hbl hornblende pyroxenite pyroxene hornblendite Px Ol Px plagioclase-bearing plagioclase-bearing Hbl orthopyroxenite clinopyroxenite pyroxenite hornblendite pyroxenite hornblendite.