A very pure tellurium crystal

Tellurium is a chemical element. It has the chemical symbol Te and the atomic number 52. It has 52 protons and 52 electrons. Its mass number is 127.6. It has 8 natural isotopes. 4 are stable and 4 are radioactive. One of the radioactive ones lasts longer than any other isotope. It has a half life of 2.2 x 10²⁴ years (2.2 septillion years).