Which statement best describes a growth sector in crystallography?

• A. A two-dimensional growth line on a crystal surface
• B. A region where growth is suppressed
• C. A flat facet formed during growth
• D. A three-dimensional region with a common crystallographic growth plane

Answer: (D)

Growth sectors occur because different crystallographic planes promote growth at different rates, creating distinct three-dimensional regions of the crystal. A growth sector is the portion of the crystal whose growth is governed by one specific crystallographic plane, so the region that forms has a common growth-plane orientation throughout. That makes a three-dimensional region with a shared crystallographic growth plane the best description of a growth sector. The other options describe surface lines, zones of suppressed growth, or single flat facets, which are not the three-dimensional sectors bounded by a single growth-plane orientation.