A crystal formation in the microstructure of a metal that occurs when a new solid phase forms from a parent solid phase, such as ferrite from austenite. The new phase generally develops plates parallel to lattice planes of a single form in the parent phase, as in the four families of octahedral planes in austenite. On the polished and etched surface the traces of the plates intersect in a geometrical pattern. Needles and polyhedra may also form. The orientation of the lattice in the new phase is related to the orientation of the lattice in the parent phase. This structure is frequently seen in cast steel and in overheated wrought steel that cools too quickly, but may occur in any alloy in which a phase change occurs.