Concrete may be synonymous with its common gray hue, but pigment experimentation with the material has taken place since the ’50s. While rare, black concrete can be made by adding iron oxide, which is found naturally in magnetite—one of the most common iron ores. “When added to the concrete mix, the iron oxide particles encompass and coat the cement particles, which are 10 times smaller.” To make even darker concrete, carbon black can be used. “While iron oxide pigments bond to cement and become a permanent part of the concrete matrix, carbon black does not,” which means this kind of concrete fades more quickly. Structurally, these concretes will function just the same, but as ArchDaily says, black concrete combines two things architects commonly adore. Take a look there to learn more about the process, and see some of their favorite black concrete structures.