Diamond is made of pure carbon. The hardness and optical properties of diamond are unique because of its compact, tightly bonded crystalline structure. The conditions needed to produce this structure were for many years believed to be very high temperature and pressure, similar to the growth environment for natural diamonds.

synthetic diamond, man-made diamond that is usually produced by subjecting graphite to very high temperatures and pressures. Synthetic diamond resembles natural diamond in most fundamental properties, retaining the extreme hardness, broad transparency (when pure), high thermal conductivity, and high electrical resistivity for which diamond is highly prized.
Optical Properties of Diamond:
- Brilliance diamond has extremely high reflectivity, its reflection critical angle is small, the range of total reflection is wide, light is prone to total reflection, and the amount of reflected light is large, thus producing high brightness.
- Scintillation: The flicker of diamond is flash, that is, the reflection and flash of white light on its surface when the diamond or the light source and the observer move relatively. Colorless, transparent, well-crystallized octahedron or curved poly-shaped diamond, even without cutting and grinding, it can show good flashing light.
- Dispersion or fire: Diamond's diverse crystal faces are like a prism, which can decompose the white light that enters the crystal through refraction, reflection and total reflection into the constituent colors of white light-red, orange, yellow, green, Blue, indigo, purple and other shades.
- Luster: The outstandingly hard, smooth and shiny crystal surface or cleavage surface of corundum has a particularly strong reflection effect on white light, and this very characteristic reflection effect is called diamond luster.