Answer: An igneous rock that cools rapidly is made of really small mineral crystals.
Step-by-step explanation:
The layers inside the earth are hot enough to melt a rock. The liquid or molten rock is known as magma.
When a molten rock cools and solidifies, it results in the formation of an igneous rock.
The slow cooling of magma will result in the formation of an igneous rock with large crystals. Whereas, rapid cooling of lava will result in the formation of an igneous rock with small crystals.
Thus, it can be concluded that an igneous rock that cools rapidly is made of really small mineral crystals.