  Maps of estimated dust column density in molecular clouds are usually assumed
to reliably trace the total gas column density structure. In this work we
present results showing a clear discrepancy between the dust and the gas
distribution in the Taurus molecular cloud complex. We compute the power
spectrum of a 2MASS extinction map of the Taurus region and find it is much
shallower than the power spectrum of a 13CO map of the same region previously
analyzed. This discrepancy may be explained as the effect of grain growth on
the grain extinction efficiency. However, this would require a wide range of
maximum grain sizes, which is ruled out based on constraints from the
extinction curve and the available grain models. We show that major effects due
to CO formation and depletion are also ruled out. Our result may therefore
suggest the existence of intrinsic spatial fluctuations of the dust to gas
ratio, with amplitude increasing toward smaller scales. Preliminary results of
numerical simulations of trajectories of inertial particles in turbulent flows
illustrate how the process of clustering of dust grains by the cloud turbulence
may lead to observable effects. However, these results cannot be directly
applied to large scale supersonic and magnetized turbulence at present.
