Melting experiments on samples of basaltic rock from a thick lava now reveal that when this lava originally began to crystallize, feldspar crystals linked together to form a continuous three-dimensional network of chains when the lava was no more than 25% crystallized. Formation of this network has profound implications for the behaviour and differentiation of basaltic magma. Much of the compositional variation of igneous rocks results from the separation of liquid from crystals, a process that is dramatically affected according to whether crystals occur separately or are linked together in networks.