A diamond is a solid form of pure **carbon**, with its atoms arranged in a specific crystal structure known as diamond cubic. Cut is often considered the most important C, as it directly influences how the diamond interacts with light. A well-cut diamond maximizes: The reflection of white light. The dispersion of light into colors of the rainbow. The sparkle or flashes of light when the diamond moves. Excellent, Very Good, Good, Fair, Poor. (Note: Grading is usually only applied to round brilliant diamonds).