A chemical element, Te, atomic number 52, and atomic weight 127.60. There are eight stable isotopes of natural tellurium. Tellurium makes up approximately 10⁻⁹ % of the Earth's igneous rock. It is found as the free element, sometimes associated with selenium. It is more often found as the telluride sylvanite (graphic tellurium), nagyagite (black tellurium), hessite, tetradymite, altaite, coloradoite, and other silver-gold tellurides, as well as the oxide, tellurium ocher.