A geologist discovers a sample of fine-grained rock made up of very small crystals. Based on its physical appearance, what can the geologist conclude about the rock?

A. It formed from magma that cooled slowly.

B. It formed from the remains of living organisms.

C. It formed from materials produced by living organisms.

D. It formed from magma that cooled quickly.

D. It formed from magma that cooled quickly

Explanation:

From several experiments, geologists have come to terms with the fact that when magma cools rapidly, it does not give room for large and big sized crystals to form. Instead, tiny, little crystals would be formed.

For example, obsidian and most volcanic rocks.

When a magma has enough time to cool and solidify, we see very big crystals of minerals in them.