The boundary to the continent of stability is determined by the situations where the Coulomb energy due to electric charge overcomes the binding energy, or where decay into atomic nuclei results in lower energy. The lowest energy mass number is proportional to the cube of the charge (atomic number). However, a range of charges is stable for each mass, and the range increases as the mass increases. This can result in very heavy nuclides with atomic numbers the same as existing known elements, and even zero-charge pieces of quark matter.