Book 27, Question 34
How can a paper-thin slice of rock show its crystals?
Geologists cut a very thin slice of rock, only about as thick as a hair, and glue it to a piece of glass.
At that thickness, light can pass through the crystals. Under a special microscope with polarized light, each mineral shows its own colors and patterns. By looking at the size, shape, and colors of the crystals, geologists can name the minerals and learn how the rock formed.