uranium is a chemical element (a metal) on the periodic table. it has an atomic number of 92, which means that a uranium atom has 92 protons in its center, which is called a nucleus. uranium that is dug out of the ground will be made from three different isotopes: three different types of uranium with different numbers of neutrons in their nuclei. most of it is uranium-238; uranium-235 is less common; uranium-234 is the rarest. pitchblende is the main ore that is mined for uranium.