  We analyze the interference field formed by two electromagnetic plane waves
(with the same frequency but different wave vectors), and find that such field
reveals a rich and highly non-trivial structure of the local momentum and spin
densities. Despite the seemingly-planar and extensively-studied character of
the two-wave system, we find that it possesses a transverse (out-of-plane)
helicity-independent spin density, and also a transverse polarization-dependent
momentum density with unusual physical properties. The polarization-dependent
transverse momentum represents the so-called Belinfante spin momentum, which
does not exert the usual optical pressure and it is considered as `virtual' in
field theory. We perform analytical estimations and exact numerical simulations
of the interaction of the two-wave field with probe Mie particles. The results
of these calculations clearly indicate the straightforward detectability of the
unusual spin and momentum properties in the two-wave field and strongly
motivate their future experimental verifications.
