Crystalline describes something made of crystals or having the clear, orderly structure of a crystal. When you look at a snowflake under a microscope, you see its crystalline structure: perfectly geometric patterns where water molecules have arranged themselves in precise, repeating shapes. Sugar, salt, and diamonds all have crystalline structures too, which is why they can form beautiful, angular shapes with flat faces and sharp edges.

Scientists use crystalline to describe materials where atoms or molecules line up in regular, repeating patterns, like soldiers standing in perfect formation. This orderly arrangement gives crystalline materials special properties. Salt crystals break along straight lines. Quartz crystals can be so clear that light passes through them easily. When something is crystalline, its internal order often shows on the outside through its shape and appearance.

The word also describes things that are exceptionally clear or pure, like crystalline water in a mountain stream. When a bell produces a crystalline tone, the sound is clear, bright, and pure. A singer might have a crystalline voice that sounds perfectly clear and beautiful, like light passing through a perfect diamond.