A network of cracks pervading a rock is modeled by a random distribution of two-dimensional intersecting, complex, narrow cracks. The percolation properties of the resulting network are studied as functions of the crack-area density and size of the medium. Gas flow commences at a finite value of the crack density which in Arkansas Novaculite rocks amounts according to our model to 670 cracks per cm2. The mean probability of finding at least one crack intersecting another is 0.57 at the threshold density. Above that, the rock gas-flow permeability increases superlinearly with crack density due to the enhancement of short percolative paths.

We derive the number and weight distributions of fragment pieces (of linear size a) that are obtained in a sudden fragmentation process. The information-entropic derivation is based on a fragment energy e(a) which incorporates the physical mechanisms and material properties responsible for breakage. For not too large fragments the number distribution follows a power law a−Θ, where Θ is between 2 and 5, depending on the size range and circumstances of the breakage. Our results are compared with other theories of size distributions.

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