Black Agate Rings: The Dark and Enigmatic Stone An unusual chalcedony stone forged in volcanic rock, Black Agate is a member of the family of Agate. Mexico, Brazil, the United States, Uruguay, and Madagascar are the countries that use dark and enigmatic stones the most. A glossy black, black agate ring is mysterious and enigmatic. Only when the stone is illuminated does the utter darkness of it become lessened. There, the actual transparency of it is revealed. Strength, emotional harmony, and stability are central to black agate's primary meaning.