Ever since Mr. Big proposed to Carrie Bradshaw in Sex and the City 2 with one, the black diamond engagement ring has been gaining devotees. Attribute the trend to Carrie’s enduring fashion influence, or simply to a growing love of the look itself. Nothing says you’re one of a kind like a gem the color of the midnight skies. If your taste is more rarified than your budget and you’re seeking a black diamond engagement ring, you may want to opt for a white sparkler that has been heat-treated to turn the darker hue. Naturally occurring black diamonds are incredibly scarce (some scientists say a supernova created them billions of years ago!) and wildly expensive.