  We introduce a model system of anisotropic colloidal `rocks'. Due to their
shape, the bonding introduced via non-absorbing polymers is profoundly
different from spherical particles: bonds between rocks are rigid against
rotation, leading to strong frustration. We develop a geometric model which
captures the essence of the rocks. Experiments and simulations show that the
colloid geometry leads to structures of low fractal dimension. This is in stark
contrast to gels of spheres, whose rigidity results from locally dense regions.
At high density the rocks form a quasi one-component glass.
