A crystal is a solid material whose atoms or molecules are arranged in a highly organized, repeating pattern that extends in all directions. This ordered structure gives crystals their characteristic flat surfaces and geometric shapes. Table salt forms tiny cube-shaped crystals. Snowflakes are ice crystals with six-sided symmetry. Diamonds, rubies, and emeralds are precious crystals valued for their beauty and durability.

You can grow crystals at home by dissolving sugar or salt in hot water and letting the water evaporate slowly. As the water disappears, the dissolved substance arranges itself into orderly patterns, forming visible crystals. Rock collectors prize mineral crystals like quartz, amethyst, and geodes, which form naturally underground over thousands or millions of years as minerals cool and solidify.

The word crystal also describes anything exceptionally clear and transparent, like crystal-clear water in a mountain stream or a crystal-clear explanation that's perfectly easy to understand. This meaning comes from quartz crystal, which can be as transparent as glass.

As an adjective, crystal can describe something made of this kind of glass, as in crystal goblets or a crystal chandelier. Though not technically crystals in the scientific sense, they earned their name because they sparkle brilliantly when light passes through them, much like natural crystals catching sunlight.