Asteroids of this class have
spectra very similar to those of
carbonaceous chondrite meteorites (types CI and CM). The latter are very close in chemical composition to the
Sun and the primitive
solar nebula minus
hydrogen,
helium and other volatiles.
Hydrated (water-containing) minerals are present. C-type asteroids are extremely dark, with
albedos typically in the 0.03 to 0.10 range. Consequently, whereas a number of
S-type asteroids can normally be viewed with
binoculars at
opposition, even the largest C-type asteroids require a small
telescope. The potentially brightest C-type asteroid is
324 Bamberga, but that object's very high
eccentricity means it rarely reaches its maximum
magnitude. Their
spectra contain moderately strong
ultraviolet absorption at wavelengths below about 0.4 μm to 0.5 μm, while at longer wavelengths they are largely featureless but slightly reddish. The so-called "water" absorption feature of around 3 μm, which can be an indication of water content in minerals, is also present. Due to their volatile-rich (icy) composition, C-type asteroids have relatively low density. A survey of 20 C-type asteroids found an average density of . The largest unequivocally C-type asteroid is
10 Hygiea, although the
SMASS classification places the largest asteroid,
1 Ceres, here as well, because that scheme lacks a
G-type. == C-group classifications ==