The asteroid belt is composed of three types of asteroid: C-type (carbonaceous, ~75 percent of all asteroids), S-type (silicate-rich, ~17 percent of asteroids) and M-type (metal-rich), which are roughly 10 percent of the total population. The numbers, in this case, don’t add up to 100 percent because we aren’t sure of the exact ratios. 16 Psyche is an M-type asteroid made of iron-nickel. What makes it unusual is that it’s believed to be the now-exposed core of a protoplanet. It’s also estimated to be worth $10,000 quadrillion dollars, if anybody has a towing hitch handy.