Obsidian.

Is organic glass of a  same kind  mountain breed of dark shadows, as half transparent, grey colour of different colours of light till black almost, as used for a magic rituals, as items of this stones are strong amulets.As attentions for astral force, care of full acts, as of fullness, as loosing possibles for sin, as suppressing aggressive energy, rising sharpness of mind, helping to see an own limits , as a saver stone for Aquarius, as for amulet, and for Sagitarius, Leo, Capricorn as carry this stone of silver ring, as they are more confidence in itself, rising attention concentration, collected.
As affecting on the sacrum chakra Muladhara, for an energy body charging  his apply on the navel or groin, as pieces of stone are for central along body, as smoothing energy of meridians, as rising immunity, physical forces, vital tone, concentration attention, lowering strain, as good who dreaming in slimming, curing urinary ways, affecting and on the stomach, bowel, liver, stabilizing blood pressure, if carry constantly are beads of obsidian, or bracelet, strengthening immunity, good are for kidneys.