There are at least five taxonomic classification systems used by various camps (see Tholen & Barucci). In Tholen's scheme,there are at least 14 asteroid classes, based on albedo and spectral characteristics. However, most asteroids fall into one of the following classes:

Class	albedo	spectrum	surface mineralogy[a]
C	low	flat to slightly reddish	hydrated silicates + carbon, organics
D	low	featureless, slightly red shortward of 5500 Å, very red longward of 5500 Å	carbon, organic-rich silicates?
P	low	featureless, flat, intermediate between C and D	carbon, organic-rich silicates?
M	moderate	featureless, flat	metal (possible trace silicates)
S	moderate	moderate to strong absorption feature shortward of 7000 Å	metal + olivine + pyroxene

Birlan et al. performed a multivariate statistical analysis to determine asteroid reflection spectra in an automated manner, as opposed to the usual "by hand" approach of classification. One of the most interesting findings from this study is that infrared colors are very important in discriminating between the various asteroid types.

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