All pendulums vary in size and color.
Pendulum divination is a very simple form of divination that relies heavily on yes/no answers to questions about things that are and things that may come to pass. A pendulum of some sort is tied to a string or chain and held in one hand. As the question is asked, the answer comes in the form of the pendulum swinging north/south, east/west, or in circles of some sort. Mats or predeterminded directions are used for the yes/no validation.
Obsidian is a protective stone that can be used to guard against all forms of negativity and in spells designed to remove negativity from a person, object or area.
Obsidian jewelry can be worn to protect against psychic attack and obsidian blades can be used in rituals to cut unwanted links between people.
Obsidian cut into the shape of an arrowhead is a powerful protective amulet. Place four obsidian arrowheads around your home, pointing in the four cardinal directions for protection.
Obsidian is also useful for grounding.