Pendulums are divination tools, used to answer yes/no questions to assist in providing direction.  They work by responding to your subconscious mind.
 
Black Amethyst
Origin: India
Associated with Crown & Root chakras
Contains Hematite in the Amethyst stone giving the darker colour.  This results in a grounding stone that connects the crown & root chakras.  Especially helpful for stress, trauma, balancing, and pain.
 
This listing is for 1 pendulum intuitively chosen by me.