Examkin

Question

Difficulty: EasyRocks, Minerals, and Soil

Molten rock deep beneath Earth's surface cools very slowly over thousands of years, allowing large and visible mineral crystals to develop. Which type of rock is formed by this process?

  1. A
    Clastic sedimentary rock
  2. B
    Extrusive igneous rock
  3. Intrusive igneous rockAnswer
  4. D
    Foliated metamorphic rock

Answer

Intrusive igneous rock
Intrusive igneous rocks (such as granite) form when magma remains trapped deep beneath Earth's crust. Because the surrounding rock acts as an insulator, the magma cools very slowly, giving individual minerals sufficient time to grow into large, interlocked, visible crystals.

Step-by-Step Solution

1
Identify the primary origin of the rock material from the description.
The rock forms directly from the cooling and solidification of molten rock (magma).
Rocks that solidify from molten material are classified into the igneous family.
2
Determine the effect of location and cooling rate on crystal texture.
Subsurface magma cools at a slow rate, granting mineral crystals sufficient time to grow large and coarse.
Slow cooling beneath the surface characterizes intrusive (plutonic) igneous rocks, whereas rapid surface cooling produces extrusive igneous rocks.

Key Concept

Igneous rock classification by formation environment and cooling rate
Estimated Time:45s
Rate this question

Topics

Rocks, Minerals, and Soil

More questions from this topic