AGATE - is a variegated class of chalcedony, usually exhibiting colored bands or other markings.  CALCITE -a mineral that releases electrical impulses when placed under pressure, and is an energy amplifier.  It helps the mind and body to remember. Calcite is a world teacher for all of humanity, facilitating awareness and appreciation of the creative forces of nature.  OBSIDIAN - is lustrous volcanic glass, the color range and related names are varied. It provides a shield against negativity. Black Obsidian used to produce sincerity in action and insight into future scenes and symptoms.  Mahogany Obsidian occurs as a combination of the colors red brown and black.  It can stimulate growth of the physical, emotional, intellectual and spiritual centers and to provide strength in times of need. Snowflake Obsidian is a stone of purity, bringing both purity and balance to the body, mind, and spirit.  It can be used in the treatment of disorders of the veins the skeletal structure, and to clear the eyes.  ONYX - is a type of chalcedony which occurs, usually, in the form of layers of a variety of colors.  It can be used to banish grief, to enhance self-control, to stimulate the power of wise decision making and to encourage happiness and good fortune.