We have measured extremely large coercive magnetic fields of up to 55~T in Sr3NiIrO6, with a switched magnetic moment ≈0.8 μB per formula unit. As far as we are aware, this is the largest coercive field observed thus far. This extraordinarily hard magnetism has a completely different origin from that found in conventional ferromagnets. Instead, it is due to the evolution of a frustrated antiferromagnetic state in the presence of strong magnetocrystalline anisotropy due to the overlap of spatially-extended Ir4+ 5d orbitals with oxygen 2p and Ni2+ 3d orbitals. This work highlights the unusual physics that can result from combining the extended 5d orbitals in Ir4+ with the frustrated behaviour of triangular lattice antiferromagnets.