!--------1---------2---------3---------4---------5---------6---------7---------8
function heat_decay(time,i)
  use global_constants, only : rkind, density, volume_ratio_rock, year, density_rock_hydrous
  use heat_radiogenic, only : heatAl, iAl, lambdaAl, mass_ratio_Al &
    & , mass_ratio_Al_hydrous, heatFe, lambdaFe, mass_ratio_Fe, mass_ratio_Fe_hydrous &
    & , heatK, lambdaK, mass_ratio_K, mass_ratio_K_hydrous
  use material_parameters, only : mn, mass_ratio_rock, mass_ratio_water &
    & , mass_ratio_anhydrous_rock, mass_ratio_hydrous_rock, mass_ratio_dehydration_rock
  implicit none
  integer,intent(in) :: i
  real(rkind),intent(in) :: time
  real(rkind) :: heat_decay, heat_decay_anhydrous, heat_decay_hydrous &
    & , heat_decayAl, heat_decayFe, heat_decayK , Tdensity
  heat_decayAl = heatAl(iAl)*exp(-lambdaAl*time)
  heat_decayFe = heatFe(iAl)*exp(-lambdaFe*time)
  heat_decayK = heatK(iAl)*exp(-lambdaK*time)
  heat_decay_anhydrous = heat_decayAl*mass_ratio_Al + heat_decayFe*mass_ratio_Fe &
    & + heat_decayK*mass_ratio_K
  heat_decay_hydrous = heat_decayAl*mass_ratio_Al_hydrous & 
    & + heat_decayFe*mass_ratio_Fe_hydrous + heat_decayK*mass_ratio_K_hydrous
  if(mn(i) == 1 .AND. mn(i) == 2 .AND. mn(i) == 3) then
    return 
  elseif(mn(i) /= 7 .AND. mn(i) /= 8 .AND. mn(i) /= 11 &
    & .AND. mn(i) /= 15 .AND. mn(i) /= 16 .AND. mn(i) /= 17) then
    heat_decay = Tdensity(i) &
      & *(mass_ratio_anhydrous_rock(i)*heat_decay_anhydrous &
      & + mass_ratio_hydrous_rock(i)*heat_decay_hydrous) 
  elseif(mn(i) == 7) then
    heat_decay = density(6) &
      & *(mass_ratio_anhydrous_rock(i)*heat_decay_anhydrous &
      & + mass_ratio_hydrous_rock(i)*heat_decay_hydrous) 
  elseif(mn(i) >= 15) then
    heat_decay = Tdensity(i) &
      & *(mass_ratio_anhydrous_rock(i)*heat_decay_anhydrous &
      & + mass_ratio_hydrous_rock(i)*heat_decay_hydrous &
      & + mass_ratio_dehydration_rock(i)*heat_decay_hydrous)
  elseif(mn(i) == 8) then
    heat_decay = density(4)*volume_ratio_rock(8)*heat_decay_anhydrous 
  elseif(mn(i) == 11) then
    heat_decay = density(4)*volume_ratio_rock(11)*heat_decay_anhydrous 
  else
    call log_error(i,'heat_decay mn8 check')
    return
  endif
  return
end function heat_decay