Rainbow moonstone pendulum - it's used as a channel for energy, and is one form of "dowsing," which is a technique for searching for anything invisible, and by observing the motion of a pointer ... or the changes in direction of a pendulum, in response to unseen energy.
Dowsing has been relied upon for centuries, and was historically used to help people find underground water sources and minerals like gold.
All crystal pendulums will differ, due to the natural formations.