Diamonds have been the most precious gems since ancient times, with transparent, flawless, colorless or slightly blue as the top grade. ※. The finished product is called a diamond.

Diamonds are colorless, transparent or slightly blue, yellow, brown, gray, black and other colors. Gray or black round diamonds are called black diamonds. Some diamonds can be changed manually, and the refractive index of standard diamond luster is as high as 2.40 ~ 2.48. It has a strong dispersion. Under X-ray irradiation, it emits blue-green fluorescence and is used for mineral processing. Octahedral cleavage is medium. The specific gravity of the best quality diamond can reach 3.53, while that of the black diamond is only 3. 15. Mohs hardness is 10, which is the highest hardness among known substances. Semiconductors. When diamond is heated to 1000℃, it can be slowly transformed into graphite.

■ Mohs hardness scale

Gypsum/1.2- 1. Talc 2. plaster

Fang Ying /3.4-3. Calcite 4. fluorite

Phosphorus length /5.6-5. Apatite 6. orthoclase

King /7.8-7. Timely 8. topaz

Yu Gang /9. 10-9. Corundum 10. diamond