The geometry of the vein system in ice has been investigated using photographs of enlarged veins in ice samples that were grown in the laboratory. The veins, which are non-uniform, act as tiny triangular-shaped, water-filled prisms that refract the light passing through them.
The three vein widths in the cross-section of a vein can be deduced from two photographs taken from different directions. The dihedral angle along a given vein edge can be observed directly by viewing it at a node, where four veins meet, from a particular direction. The dihedral angles range from 25° ± 1° to 105° ± 1°. It is shown that the vein cross-section can be constructed, given the three widths of a vein and one of the dihedral angles, providing that the radius of curvature around the vein wallsr
v is a constant. This assumption can be checked if the values of at least two of the dihedral angles associated with the vein cross-section are known. Ifr
v is a constant, then the solid-liquid interfacial energy ϒ
sl must be isotropic for the veins in question and any deviations from uniform equilibrium geometry must derive primarily from anisotropy in the grain-boundary energy ϒ
ss. The cross-sections of three veins that meet in a particular node are constructed. The assumption of isotropic ϒ
sl is found to hold for this node.