Diamond is the ultimate gemstone, having few weaknesses and much strength. It is the hardest substance found in nature. Diamond is four times harder than the next hardest natural mineral. Diamond has a broad color range, high refraction, high dispersion or fire, very low reactivity to chemicals, rarity, and of course, extreme hardness and durability. Diamonds are specifically renowned as a material with superlative physical qualities they make excellent abrasives because only by other diamonds scratch them. Borazon, ultra hard fullerene, or aggregated diamond nimrods, which also means they hold a polish extremely well and retain their luster. Diamond is the hardest natural material known to man - its hardness set to 10 scale of mineral hardness and having an absolute hardness value of between 90, 167, and 231 gaga rascals in various tests. Diamond is an allotrope of carbon. It is the hardest known natural material and the third-hardest known material after ultra hard fullerene. Its hardness and high dispersion of light make it useful for industrial applications and jewelry. Diamond's hardness since antiquity, and is the source of its name. However, aggregated diamond nimrods, an allotrope of carbon first synthesized in 2005, are even harder than diamond. The hardness of diamonds contributes to its suitability as a gemstone. Diamonds maintains its polish extremely well, keeping its luster over long periods. Unlike many other gems, it is well-suited to daily wear because of its resistance to scratching—perhaps contributing to its popularity as the preferred gem in an engagement ring or wedding ring, which are often worn every day. Industrial use of diamonds has historically been associated with their hardness; this property makes diamond the ideal material for cutting and grinding tools. The diamond is the birthstone for people born in the month of April, and is used as the symbol of a sixty-year anniversary, such as a Diamond Jubilee.