Which feature is a triangular depression or protrusion on a diamond's octahedral faces?

Which feature is a triangular depression or protrusion on a diamond's octahedral faces?

• A. A triangular facet on the diamond's pavilion.
• B. A triangular arrangement of lattice points.
• C. A triangular depression or protrusion on a diamond's octahedral faces.
• D. A triangular cut feature used in gem cutting.

Answer: (C)

The main idea is recognizing a specific crystal-growth feature on the diamond’s surface. On the octahedral faces (the {111} faces) of a diamond, triangular growth markings can appear as depressions or small protrusions. These are called trigons. They form because of how atoms attach and arrange during natural growth on the octahedral planes, and they can show up as either pits or raised triangles aligned with the crystal’s threefold symmetry. This feature is a natural surface characteristic, not something produced by cutting. That’s why it’s distinct from a triangular facet created during gem cutting or a triangular pattern described in lattice terms.

The main idea is recognizing a specific crystal-growth feature on the diamond’s surface. On the octahedral faces (the {111} faces) of a diamond, triangular growth markings can appear as depressions or small protrusions. These are called trigons. They form because of how atoms attach and arrange during natural growth on the octahedral planes, and they can show up as either pits or raised triangles aligned with the crystal’s threefold symmetry.

This feature is a natural surface characteristic, not something produced by cutting. That’s why it’s distinct from a triangular facet created during gem cutting or a triangular pattern described in lattice terms.