Extrusive Rocks: Fine Grains or No Crystals?

What type of grains do extrusive rocks that cool quickly have?

a) Fine grains or no crystals.

Answer:

Extrusive rocks that cool rapidly tend to have fine grains or no crystals due to the quick cooling process which limits crystal formation.

Extrusive rocks that cool quickly tend to have fine grains or no crystals. This happens due to the rapid cooling, which prevents the formation of large crystals. An example is basaltic lava, which flows quickly and cools swiftly once it reaches the surface. This rapid cooling allows the formation of very small crystals or none at all, resulting in a generally fine-grained texture.

Unlike intrusive rocks which form beneath the surface of the earth and have sufficient time to form large crystals, the rapid exposure of extrusive rocks to the cooler environment on earth's surface speed up the cooling process, reducing the time for large crystal formation.