What is the most important factor that controls the size of mineral grains in an igneous rock?

Question

Quizplus · Accepted Answer

The rate of magma cooling is the most important factor that controls the size of mineral grains in an igneous rock. Rapid cooling results in small grains, while slow cooling results in large grains. Other factors, such as magma composition and plate tectonic environment, can influence the types of minerals that form but have less impact on the size of the mineral grains. The iron content of minerals can affect their color but does not control the size of the grains.

What Is the Most Important Factor That Controls the Size