List the light-colored silicate minerals. List the dark-colored silicate minerals. Distinguish between intrusive and extrusive igneous rocks. Examine the table below, from Volcano World. Classification of volcanic rocks by silica content.
All numbers are in weight percent.
Values are weight percent oxide. Tholeiitic basalts have low alkali element contents relative to alkali basalts at the same silica content. The relationship between eruptive stage and composition of rocks from specific volcanoes is explored in this activity. A plot of silica versus alkali element content is shown in activity 9. Examine the graph and answer the questions from Volcano World.