Made of Artificial tiger's eye gemstone quartz. Polished smooth surface, each ball size approx: 1.75' in diameter Develops nimble fingers and hand coordination, through rhythmic flexing of wrist, fingers, hand and arm tendons Stimulates the meridians that flow into the fingers, ideal warm-up exercise before activities such as painting, piano playing, calligraphy etc.. A set of two balls come in a beautiful gift box!