  Spacetimes with a vanishing second Ricci invariant, but which are not
necessarily Ricci - flat, though common in general relativity, are seldom
studied in a coordinate and symmetry independent way by actually using their
Ricci invariants. Yet, and as an example, it can be shown by use of Ricci
invariants that no such spacetimes can actually represent a perfect fluid by
way of Einstein's equations. The widely studied Kiselev black hole is a
particularly simple example of such a spacetime. Yet it is frequently, and
erroneously, referred to as a perfect fluid. This paper gathers together
information relevant to the study of spacetimes with vanishing a second Ricci
invariant. It is shown that such spacetimes need not be stationary, a point
relevant to their possible physical significance.
