Answer to Question #88 in Molecular Physics | Thermodynamics for Mary
A block, carved from a single crystal, while being heated, can turn into a parallelepiped. Why is this possible?
Single crystals may have different internal symmetry, and their coefficients of expansion along different directions of symmetry are also different. A block will remain the shape of a cube only if it is made from an amorphous body (without symmetry), or a cubic crystal (all directions are equal).