Dioptase

Dioptase is an intense emerald to bluish-green copper silicate with a hardness of about five. Wikipedia lists its colour as dark teal to emerald green. Hall describes brilliant small crystals on a matrix, or a non-crystalline mass, in a deep bluish green or emerald. Hall calls it a strong healer of the heart, and associates it with living in the present moment, recalling past lives, dissolving grief, betrayal and sorrow, and opening psychic vision when placed on the third eye. She also says it works well as a gem essence. These are Hall's claims, not established fact. Wikipedia warns that dioptase dust is toxic because of its copper content, and that swallowing it by accident can cause serious illness.