Rocks that cooled so quickly at the surface that they have small mineral grains or a glassy texture are called

Rocks that cooled so quickly at the surface that they have small mineral grains or a glassy texture are called

• A. Intrusive
• B. Extrusive
• C. Sedimentary
• D. Metamorphic

Answer: (B)

Rocks that crystallize at the surface from lava cool very quickly, so crystals don’t have time to grow and you end up with tiny mineral grains (aphanitic texture) or a glassy texture if cooling is extremely rapid. That rapid surface cooling points to an extrusive igneous rock, formed when magma erupts and solidifies at or near the surface. In contrast, rocks that solidify underground cool slowly and develop large crystals (intrusive). Sedimentary rocks come from pressed and cemented sediments, not from cooling magma, and metamorphic rocks form from existing rocks altered by heat and pressure. So the described texture matches extrusive rocks.

Rocks that crystallize at the surface from lava cool very quickly, so crystals don’t have time to grow and you end up with tiny mineral grains (aphanitic texture) or a glassy texture if cooling is extremely rapid. That rapid surface cooling points to an extrusive igneous rock, formed when magma erupts and solidifies at or near the surface. In contrast, rocks that solidify underground cool slowly and develop large crystals (intrusive). Sedimentary rocks come from pressed and cemented sediments, not from cooling magma, and metamorphic rocks form from existing rocks altered by heat and pressure. So the described texture matches extrusive rocks.