What term refers to colorless lines or grooves on a diamond crystal's surface?

• A. A type of gemstone cut.
• B. The internal lattice spacing.
• C. Colorless lines or grooves on a diamond crystal's surface.
• D. A trace element.

Answer: (C)

Graining describes the natural lines that form as a diamond crystal grows. These lines can appear on the surface as colorless lines or grooves when light interacts with the crystal. They arise from irregular growth within the crystal’s lattice and may run in specific directions. They’re internal features that show up on the surface, not something related to how the stone is cut, nor to atomic spacing or impurities. So the term that matches “colorless lines or grooves on a diamond crystal’s surface” is graining.