  We present an extensive study of 72 archival Chandra light curves of the
high-frequency-peaked type blazar Mrk 421, the first strong extragalactic
object to be detected at TeV energies. Between 2000 and 2015 Mrk 421 often
displayed intraday variability in the 0.3-10.0 keV energy range, as quantified
through fractional variability amplitudes that range up to 21.3 per cent. A
variability duty cycle of ~84 per cent is present in these data. Variability
timescales, with values ranging from 5.5 to 30.5 ks, appear to be present in
seven of these observations. Discrete correlation function analyses show
positive correlations between the soft (0.3-2.0 keV) and hard (2.0-10.0 keV)
X-ray energy bands with zero time lags, indicating that very similar electron
populations are responsible for the emission of all the X-rays observed by
Chandra. The hardness ratios of this X-ray emission indicate a general
"harder-when-brighter" trend in the spectral behaviour of Mrk 421. Spectral
index-flux plots provide model independent indications of the spectral
evolution of the source and information on the X-ray emission mechanisms. Brief
discussions of theoretical models that are consistent with these observations
are given.
