  We present a new unified covariant description of electromagnetic field
properties for an arbitrary space-time. We derive a complete set of irreducible
components describing a six-dimensional electromagnetic field from the Maxwell
and metric tensors using the symmetry group SL(2,C). For the special case of a
flat space-time metric the components are shown to correspond to the scalar
invariants of the electromagnetic field, the energy-momentum-stress tensor and
in addition, three new tensors expressing physical observables of rank two and
four, respectively. We make a physical interpretation of one of the new rank
two tensors as describing a classical intrinsic spin of the electromagnetic
field.
