A diamond (from the ancient Greek ἀδάμας – adámas, meaning “unbreakable,” “proper,” or “unalterable”) is one of the best-known and most sought-after gemstones. Diamonds have been known to mankind and used as decorative items since ancient times; some of the earliest references can be traced to India. The hardness of diamond and its high dispersion of light – giving the diamond its characteristic “fire” – make it useful for industrial applications and desirable as jewelry. Diamonds are such a highly traded commodity that multiple organizations have been created for grading and certifying them based on the four Cs, which are color, cut, clarity, and carat. Other characteristics, such as presence or lack of fluorescence, also affect the desirability and thus the value of a diamond used for jewelry. Perhaps the most famous use of the diamond in jewelry is in engagement rings, which became popular in the early to mid 20th century due to an advertising campaign by the De Beers company, though diamond rings have been used to symbolize engagements since at least the 15th century. The diamond’s high value has also been the driving force behind dictators and revolutionary entities, especially in Africa, using slave and child labor to mine blood diamonds to fund conflicts.