As the silica content varies from less than 40% to more than 70% there is a systematic ________.
A)decrease in calcium, magnesium, and iron with an increase in sodium and potassium
B)increase in calcium, magnesium, and iron with a decrease in sodium and potassium
C)increase in the temperature at which point melting begins
D)decrease in the quartz content of the rocks

Question

Quizplus · Accepted Answer

As the silica (SiO2) content in igneous rocks increases, there is typically a decrease in the content of calcium, magnesium, and iron, which are components of mafic minerals, and an increase in sodium and potassium, which are components of felsic minerals. This reflects the transition from mafic rocks (low silica content) to felsic rocks (high silica content).

As the Silica Content Varies from Less Than 40% to More