Black agate is a type of chalcedony, a microcrystalline form of quartz, that is associated with many meanings and properties:
Grounding
Black agate is connected to the root chakra, which is the first chakra in the body's energy system and is associated with grounding, security, and stability.
Protection
Black agate is said to protect the wearer from danger and evil spirits, and to offer protection against curses and hexes.
Emotional healing
Black agate is said to promote emotional stability and healing, and to help clear emotional pain