  We report on the findings of a 364 ksec observation of the BL LAC object Mrk
421 with the X-ray observatory Suzaku. The analysis in this paper uses fluxes
and hardness ratios in the broad energy range from 0.5 keV to 30 keV. During
the course of the observation, the 0.5 keV - 30 keV flux decreased by a factor
of $\sim$2 and was accompanied by several large flares occurring on timescales
of a few hours. We find that fitting a broken power model to spectra from
isolated epochs during the observation describes the data well. Different
flares exhibit different spectral and hardness ratio evolutions. The cumulative
observational evidence indicates that the particle acceleration mechanism in
the Mrk 421 jet produces electron energy distributions with a modest range of
spectral indices and maximum energies. We argue that the short-timescale X-ray
spectral variability in the flares can be attributed mostly to intrinsic
changes in the acceleration process, dominating other influences such as
fluctuations in the Doppler beaming factor, or radiative cooling in or outside
the acceleration zone.
