  Dawn's framing camera observed boulders on the surface of Vesta when the
spacecraft was in its lowest orbit (LAMO). We identified, measured, and mapped
boulders in LAMO images, which have a scale of 20 m per pixel. We estimate that
our sample is virtually complete down to a boulder size of 4 pixels (80 m). The
largest boulder is a 400 m-sized block on the Marcia crater floor. Relatively
few boulders reside in a large area of relatively low albedo, surmised to be
the carbon-rich ejecta of the Veneneia basin, either because boulders form less
easily here or live shorter. By comparing the density of boulders around
craters with a known age, we find that the maximum boulder lifetime is about
300 Ma. The boulder size-frequency distribution (SFD) is generally assumed to
follow a power law. We fit power laws to the Vesta SFD by means of the maximum
likelihood method, but they do not fit well. Our analysis of power law
exponents for boulders on other small Solar System bodies suggests that the
derived exponent is primarily a function of boulder size range. The Weibull
distribution mimics this behavior and fits the Vesta boulder SFD well. The
Weibull distribution is often encountered in rock grinding experiments, and may
result from the fractal nature of cracks propagating in the rock interior. We
propose that, in general, the SFD of particles (including boulders) on the
surface of small bodies follows a Weibull distribution rather than a power law.
