A tetrahedral hole is located at the center of a tetrahedron formed by three anions in the lower layer and one anion in the top layer.

A second type of tetrahedral hole is formed by three anions in the top layer and one anion in the lower layer.

An octahedral hole is located at the center of an octahedron formed by three anions in the top layer and three anions in the lower layer.

Use the links on the right to show 2 types of tetrahedral holes, and an octahedral hole.