The fragmentation fractal has been used to accurately describe the distribution of rock progeny from single particle breakage events. This paper illustrates the underlying physical significance of the fragmentation fractal and how it may be used as a fundamental tool in understanding rock pulverisation. The experimental determination of the fragmentation fractal is based on the measurement of particle size by projected area as given by image analysis. In this format the characteristic length is defined as the square root of projected area, This approach to rock particle size analysis can have advantages over other techniques especially when the mass or number of fragments is small. A brief comparison has been made with size by projected area and the corresponding sieve size of artificial objects of different shape, but equivalent characteristic length. It is suggested that projected area measurements are less sensitive to the influence of particle shape and that this may even aid the comparison of distributions of fragments of significantly different morphologies.