C-type asteroids are asteroids made of carbonates. They are the most common variety taking up around 75% of known asteroids, and an even higher percentage in the farther part of the belt beyond 2.7 AU, which is dominated by this asteroid type. The amount of C-types may actually be higher than this, because C-types are much darker than most other asteroid types except D-types and others common only at the extreme farther edge of the Main Belt.