Which minerals are the first to crystallize in a cooling ...

[karlynnae]

Which minerals are the first to crystallize in a cooling magmaminerals with a lower percentage of silica or minerals with a higher percentage of silica?
 
  What will be an ideal response?

Question 2

How does silica content effect volcanic eruptions?
 
  What will be an ideal response?

[joneynes]

Answer to Question 1

Answer: Minerals with a lower percentage of silica.

Answer to Question 2

Answer: Silica content greatly effects magma viscosity. The greater the silica content, the greater the viscosity (resistance to flow). Magmas with a high silica content flow slowly, while magmas with a low silica content tend to flow more easily. As such, basaltic eruptions (low silica content) are very fluid while andesitic eruptions (high silica content) flow slowly. The high resistance to flow can act as a trap to gases in the magma that, as pressure builds up, can cause the volcano to erupt explosively.