Name a metal that commonly adopts a hexagonal close-packed structure.

• A. Iron
• B. Magnesium
• C. Copper
• D. Aluminum

Answer: (B)

Magnesium adopts a hexagonal close-packed lattice at room temperature, meaning its atoms stack in hexagonal layers with ABAB repeating and hexagonal symmetry. In this arrangement each atom has 12 nearest neighbors, and the conventional unit cell contains six atoms, reflecting efficient packing along the hexagonal directions. Among common metals, iron is primarily body-centered cubic at room temperature (and becomes FCC at higher temperatures), while copper and aluminum are face-centered cubic. Those cubic structures involve different stacking and slip systems than HCP, so they do not exhibit hexagonal close-packed packing. Therefore, magnesium is the metal that commonly shows hexagonal close-packed structure.