Crystal properties refer to the characteristics that define how a crystal behaves and interacts with light, heat, and other materials. These properties include hardness, cleavage, luster, and transparency. Hardness measures a crystal's resistance to scratching, while cleavage describes how it breaks along specific planes. Luster indicates how light reflects off the surface, and transparency refers to how much light can pass through the crystal. Additionally, crystals exhibit unique symmetry and structure, which are determined by their internal arrangement of atoms. This arrangement influences their color and optical properties, making each type of crystal distinct. Understanding these properties is essential in fields like mineralogy and gemology.