Cellular structures which form during the cooling of some unusual optical glasses are described. These resemble in several respects ellipsoidal structures in lava. The former are shaped by convection currents present in the cooling liquid and remain visible in the chilled material because of chemical and physical differentiation of the liquid. It is suggested that some of the structures in lava variously called ellipsoidal, pillow, or globular may have formed by convection flow modified by horizontal movement of the lava stream and followed by rather rapid quenching.