What is the softest crystal direction in a diamond called?

In the context of diamond crystallography, the softest crystal direction is referred to as the dodecahedral direction. This is significant because the structure of diamond, known for its exceptional hardness, has specific planes and orientations along which its atoms can be more easily displaced.

Dodecahedral faces, which are not as common as octahedral faces in diamond, have a unique atomic arrangement that influences how the material behaves under stress and pressure. The dodecahedral direction allows for easier ion movement, contributing to the definition of "softness" in this specific context.

While octahedral faces are the most prominent and commonly referenced directions in diamond due to their hardness characteristics, it is the dodecahedral arrangement that is identified as the softest. Both hexagonal and isometric options do not directly relate to the specific orientation considered softer in terms of crystal behavior in diamonds. Thus, the concept of the softest direction in diamond crystallography is accurately captured by identifying it with the dodecahedral structure.