  We demonstrate the abilities of elastic x-ray scattering to yield information
on dense matter with multiple ion species and on the microscopic mixing in
dense materials. Based on partial structure factors from ab initio simulations,
a novel approach for the elastic scattering feature is applied to dense
hydrogen-beryllium and hydrogen-helium mixtures. The scattering signal differs
significantly between single species, real microscopic mixtures, and two
separate fluids in the scattering volume.
