fun(?) nerd tip:
the actual reason why diamonds are so costly isn't about quality at all, the company De Beers gained a monopoly on diamond excavation well before they were popular in the public eye, and then through pr and advertisement deeply ingrained the connection between diamond rings and marriage we know today. the reason for the high price is due to artificial scarcity, they'll only put so many diamonds into circulation at a time. Also their grip on the industry is beginning to loosen since the inception of lab grown diamonds, which at this point in time can be nearly indistinguishable from natural diamonds to the trained eye.