What do you look at on the mineral to tell whether an igneous rock formed above or below the surface?

Texture and color

Explanation:

Igneous rocks form when molten rock cools and becomes solid, they are divided into two groups, based on where the rock forms:

Above the surface: these rocks are known as intrusive igneous rocks (or plutonic), they form when magma enters an underground chamber, cools very slowly, and forms rocks full of large crystals, large enough to see without a microscope, they are usually dense and dark as well. Granite is the most common type of intrusive rock. Below the surface: they are called extrusive igneous rocks (or volcanic rocks), they form when lava cools quickly, this leaves no time for elements to form minerals, therefore elements are frozen in place within the volcanic glass. They have small or no grains, are usually light-colored and have low density. Basalt is the most common type of extrusive igneous rock.

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The size of its crystals.

Explanation:

Igneous rocks origin from lava or magma, and are classified into plutonic rocks and volcanic rocks. The first origin after magma has cooled down and solidified under the surface. On the other hand, volcanic rocks consist of lava circulating on the surface that cools down and takes solid form afterward. To identify whether a rock is plutonic or volcanic, we should take a look at the size of the crystals that result from magma and lava cooling down. Plutonic rocks contain large crystals, and volcanic rocks contain small crystals.