  Highly-anisotropic in-plane magneto-resistance (MR) in graphite (HOPG)
samples has been recently observed (Y. Kopelevich et al., arXiv:1202.5642)
which is negative and linear in low fields in some current direction while it
is giant, super-linear and positive in the perpendicular direction. In the
framework of the hopping conductance theory via non-zero angular momentum
orbitals we link extraordinary MRs in graphite and in organic insulators (OMAR)
observed in about the same magnetic fields. The theory predicts quadratic
negative MR (NMR) when there is a time-reversal symmetry (TRS), and linear NMR
if TRS is broken. We argue that the observed linear NMR could be a unique
signature of the broken TRS both in graphite and organic compounds. While some
local paramagnetic centers are responsible for the broken TRS in organic
insulators, a large diamagnetism of our HOPG samples may involve a more
intriguing scenario of TRS breaking.
