Which term refers to the set of planes that are parallel and evenly spaced along crystal directions?

• A. Crystal Shape (form)
• B. Crystal Planes
• C. Glide Plane
• D. Crystal Axes

Answer: (B)

In crystallography, a group of planes that share the same orientation and are evenly spaced throughout the crystal is called crystal planes (a plane family). These planes run parallel to one another and cut the lattice at regular intervals, creating a repeating grid that extends through the structure. Each plane in the family is parallel to the others, and the spacing between adjacent planes is constant along that direction, which is a key way we describe the crystal’s internal geometry. Miller indices (hkl) are used to designate the orientation of these planes.

This term is the best fit because it specifically names the set of parallel, equally spaced planes within the crystal lattice. Other options refer to different concepts: crystal shape describes the external form of the crystal, a glide plane is a symmetry element combining reflection and translation, and crystal axes are the directional lines in the lattice, not the planes themselves.