Which crystal growth shape is most commonly associated with HPHT diamonds?

• A. Cuboctahedral
• B. Octahedral
• C. Tetrahedral
• D. Dodecahedral

Answer: (A)

Diamonds grow in a cubic lattice, so the shape you see reflects which crystal faces dominate during growth. Under HPHT conditions, growth tends to develop both the {100} faces (squares) and the {111} faces (triangles). The combination of those faces forms a cuboctahedron, a shape with both square and triangular facets. This habit appears frequently in HPHT-grown diamonds because the growth environment and catalysts favor extending along those two sets of crystallographic planes. By contrast, natural diamonds often crystallize more commonly as octahedra, and shapes like tetrahedra or dodecahedra are far less typical for HPHT synthesis. So the cuboctahedral form is the best indicator of HPHT growth.