Slow cooling below the surface results in?

Slow cooling below the surface results in?

• A. Larger mineral crystals
• B. Smaller mineral crystals
• C. Glassy texture
• D. No crystals

Answer: (A)

Cooling rate controls crystal size in igneous rocks. When magma cools slowly beneath the surface, atoms have time to migrate and join into growing crystals, so minerals become larger and the rock has a coarse-grained texture. This slow, underground cooling is typical of intrusive rocks like granite. If cooling is rapid at or near the surface, many small crystals form or a glassy texture appears if cooling is almost instantaneous. Therefore, slow cooling below the surface results in larger mineral crystals.

Cooling rate controls crystal size in igneous rocks. When magma cools slowly beneath the surface, atoms have time to migrate and join into growing crystals, so minerals become larger and the rock has a coarse-grained texture. This slow, underground cooling is typical of intrusive rocks like granite. If cooling is rapid at or near the surface, many small crystals form or a glassy texture appears if cooling is almost instantaneous. Therefore, slow cooling below the surface results in larger mineral crystals.