Which crystal planes are cleavage planes on a diamond?

• A. Cubic planes
• B. Dodecahedral planes
• C. Octahedral planes
• D. Trigonal planes

Answer: (C)

Cleavage planes in diamond follow specific crystallographic planes, reflecting how the atoms are arranged in the lattice. In the diamond cubic structure, the planes along which the crystal cleaves most easily are the octahedral planes, which correspond to the {111} family in cubic notation. These planes form the faces of an octahedron, so the term octahedral planes is used. The atomic arrangement and bond directions align to allow breaking more readily across these planes, making them the cleavage planes. Other planes, like cubic {100} or trigonal planes, do not correspond to the easy-cleavage directions in diamond.