Crystalline materials are solids where the atoms are arranged in a highly ordered, repeating pattern. This structure gives them distinct geometric shapes and contributes to their unique physical properties, such as high melting points and specific optical characteristics. Common examples of crystalline materials include salt, diamonds, and quartz. These materials can be found in various forms, including metals, minerals, and even some organic compounds. The arrangement of atoms in crystalline materials affects their strength, conductivity, and reactivity, making them essential in fields like materials science and engineering.