Classificazione Tassometrica asteroidi

 The C-Type asteroids (Carbonaceous chondrites) comprise about 75%
 of all known asteroids. Carbonaceous chondrites are very dark, with albedos ranging from 0.03 to
 0.10 (darker than charcoal), approaching soot. While named for their carbon content (typically 1% to
 2% by weight), they are noted for a high content of volatiles, generally reflecting a near-solar
 composition (minus hydrogen and helium gasses), and have a high water content (often 10%, but as
 high as 22%). They often contain 25% to 30% iron, of which 5% to 15% is in metallic grains, with the
 remainder as oxides, sulfides, or other compounds such as olivine.



The S-Type asteroids (Stony asteroids) include ordinary chondrites
 plus the achondrites, less primitive asteroids that were large enough to differentiate and to
 undergo significant thermal and/or aqueous processing (or fragments of such asteroids). All of the
 V-type asteroids, for example, are thought to be fragments of the large asteroid Vesta. S-types
 comprise about 17% of all asteroids. They have albedos ranging from 0.10 to 0.22. There are other
 well-known subgroups, including the E-types (Enstatite asteroids, highly differentiated, highly
 reduced, named for their primary mineral), and the A-Types, composed primarily of olivine, and
 thought to be fragments of planetary embryo mantles.


The stony asteroids (and meteorites derived from them) are primarily composed of silicates, with the
 actual mineral families varying according to the asteroid type. Iron content is typically 20% to
 25%, but that may primarily be as metallic iron, or as oxides, or as sulfides, or as silicates,
 depending upon the asteroid family. Iron content may be considerably lower in asteroids derived from
 highly-differentiated planetary embryos.



The M-Type asteroids (Metallic or Nickel-Iron asteroids) comprise
 about 10% of all known asteroids. They are mostly thought to be fragments of the iron cores of
 planetary embryos that were disrupted due to large collisions. As such, they are highly
 processed/differentiated, and are igneous rocks. Some are nearly pure nickel-iron alloy, although
 most have significant inclusions of graphite and silicates. Note that siderophile (iron-loving)
 metals such as gold, platinum, iridium, and palladium leach out of crustal and mantle minerals and
 concentrate in the iron cores, and thus nickel-iron asteroids are a rich source of these metals. 
The Pallasite meteorites have such a high percentage of olivine (peridot) that they are thought to
 come from the core/mantle boundaries of one or more planetary embryos. Note that a significant
 portion of the M-types may not be metallic, although they share spectral and albedo characteristics
 with metallic asteroids. For example, 22 Kalliope has only about 30% of the density of an iron
 asteroid. Kalliope and similar asteroids may be partly metallic and partly carbonaceous, or
 something else entirely.