When I was leaning Reiki My teacher was very into Crystals. She would dangle one over the various Chakras and without moving her hand (I've also experienced this) the crystal will become rather agitated (animated perhaps) and start to swing over the chakra in question which needs to be opened or energized.

Before you use the pendulum you will want to clear the energy from the Crystal. How you do this is up to you. You may want to use salt water (or boiling water)or what ever method you're comfortable for energy clearing.

Om
Mani
Padme'
Hum