  A collection of spherical particles can be packed tightly together into an
amorphous packing known as "random close packing" (RCP). This structure is of
interest as a model for the arrangement of molecules in simple liquids and
glasses, as well as the arrangement of particles in sand piles. We use confocal
microscopy to study the arrangement of colloidal particles in an experimentally
realized RCP state. We image a large volume containing more than 450,000
particles with a resolution of each particle position to better than 0.02
particle diameters. While the arrangement of the particles satisfies multiple
criteria for being random, we also observe a small fraction (less than 3%) of
tiny crystallites (4 particles or fewer). These regions pack slightly better
and are thus associated with locally higher densities. The structure factor of
our sample at long length scales is non-zero, $S(0) \approx 0.049$, suggesting
that there are long wavelength density fluctuations in our sample, perhaps due
to the tiny crystallites. Our results suggest that experimentally realizable
RCP systems may be different from simulated RCP systems, in particular, with
the presence of these long wavelength density fluctuations.
