The K3 quantity, introduced in a context of the Leggett-Garg inequality violation, is studied for the neutrino oscillations in matter with phenomenologically modelled dissipative environment. It is shown that the K3 function acquires different values depending on whether neutrino is Dirac or Majorana particle, provided that there is a dissipative interaction between matter and neutrinos. The difference occurs for various matter densities and can serve as a potential quantifier verifying the neutrino nature. Moreover, working within phenomenological model one can suggest the values of the matter density and dissipation for which the difference is the most visible. There exist also special conditions in which the violation of the Leggett-Garg inequality, to a different extent for both kinds of neutrino, is observed.