Why are the crystals of intrusive igneous rock typically larger than those of extrusive igenous rock?
a. because the magma cools very quickly
b. because the magma cools much slower
c. because of a higher water content in the magma
d. because the temperatures of the magma are much lower

Respuesta :

Intrusive rocks come from magma. They cool slowly deep in Earth's crust. When magma cools underground, the crust acts like a blanket, insulating it, keeping it warm longer. Because the magma cools slowly, crystals of different minerals have time to grow.

Intrusive igneous rock usually have larger crystals than extrusive igneous rock because b. because the magma cools much slower.

There are two types of igneous rock:

  • Extrusive igneous rock - this forms after magma erupts to the surface and cools very quickly
  • Intrusive igneous rock - this forms under the Earth's surface and so cools very slowly as temperatures underground are higher

The slow cooling time of the intrusive igneous rocks ensures that the crystals they form are much larger than those formed by the extrusive rocks which cooled too fast.

In conclusion, the magma cooling much slower under the surface leads to intrusive igneous rocks having large crystals.

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