What is one physical property other than hardness that may add to the beauty of a gemstone?

One physical property that may add to the beauty of a gemstone is its luster. Luster refers to the way light interacts with the surface of the gemstone and can range from adamantine (diamond-like) to vitreous (glass-like) to pearly or metallic. The type of luster a gemstone exhibits can greatly enhance its visual appeal and overall beauty.