  The wide-angle scattering of X-rays by anisotropic powders of nano-layered
crystallites (nano-stacks) is addressed. Assuming that the orientation
distribution probability function f of the nano-stacks only depends on the
deviation of the crystallites' orientation from a fixed reference direction, we
derive a relation providing f from the dependence of a given diffraction peak's
amplitude on the azimuthal angle. The method is applied to two systems of
Na-fluorohectorite (NaFH) clay particles, using synchrotron radiation and a
WAXS setup with a two-dimensional detector. In the first system, which consists
of dry-pressed NaFH samples, the orientation distribution probability function
corresponds to a classical uniaxial nematic order. The second system is
observed in bundles of polarized NaFH particles in silicon oil; in this case,
the nanostacks have their directors on average in a plane normal to the
reference direction, and f is a function of the angle between a nano-stack's
director and that plane. In both cases, a suitable Maier-Saupe function is
obtained for the distributions, and the reference direction is determined with
respect to the laboratory frame. The method only requires one scattering image.
Besides, consistency can be checked by determining the orientation distribution
from several diffraction peaks independently.
