B-type asteroids are relatively uncommon types of carbonaceous asteroids. B-class objects are abundant in the outer asteroid belt, and also dominate the high-inclination Pallas family which includes the second-largest asteroid 2 Pallas.
B-type asteroids are generally similar to C-type asteroids, however differ in that the ultraviolet absorption below 0.5 μm is small or absent, and the spectrum is more bluish then reddish. The albedo also tends to be greater than in the generally very dark C type.
Spectroscopy of B-type asteroids suggest they have major constituents of anhydrous silicates, organic polymers, hydrated clay minerals, magnetite, and sulfides.