A thin section is preparing a slice of rock, mineral, fossil, or bone
for microscopic examination. It's created by gluing a rock to a glass
slide, and grinding the rock until it's 30 microns thick (the average
human hair is 100 microns in diameter).
Every mineral displays different colors and optic properties under a
light microscope. This helps identify the minerals to determine the rock
composition, how it likely formed, and if any microfossils are present.