The pocket crystallophone was a musical instrument created in the early 22nd century. Also called a pocket harp or slider, the device at first appears to be a smooth stone with several parallel ridges, which respond to the touch by emitting eerie, clear tones like a glass harmonica. Technically, however, it works more similarly to a theremin in responding to the player's manipulation, but that input is used to resonate tiny glass chimes within and amplifies the resulting sound.