The most common among meteorites are chondrites. These are stone meteorites, ranging from light grey to very dark, with an amazing structure: they contain rounded chondrums grains, sometimes well visible on the surface of the fracture and easily stained with meteorite. The sizes of chondroms vary from microscopic to centimetric. They occupy a significant volume of meteorite, sometimes up to half of it, and are poorly cemented by the interchondroic matrix. The composition of the matrix is identical to, and sometimes differs from, that of the chondroma. Broken chondromas and their fragments are often found in the interchondrial chondroma.
Such a structure is inherent only in meteorites (and many of them!) and is not found anywhere else. Folded mainly by iron-magnesia silicates, chondrites also contain fine nickel-plated iron, sulfides and other minerals. There are many hypotheses about the origin of Honduras, but they are all controversial. In short, the origin of chondromas is still unknown. A distinction is made between HH, H, L and LL chondrites with very high, low and very low free metal iron content. Accordingly, the transition from one class to another reduces the total iron content (free and silicate). In addition, there is a group of E-chondrites, in which almost all iron is in a free state so that the silicates get almost one magnesium, as well as a group of carbonaceous C-chondrites, in which there is very little iron, but almost all of it is in the silicates.
Asteroid formation
During the period of formation of the Sun, the conditions in the protoplanet disk were, of course, not the same at different distances from the Sun and changed over time. The substance remained cold only far from the Sun. Near it, it was strongly warmed up and the dust was exposed to full or partial evaporation. Only later, when the gas cooled down, did it condense again, but most of the volatile substances contained in the interstellar dust was lost and no longer entered the new dust. The evolution of the protoplanetary disk led to the formation of planetesimals in it, from which the planets then grew.
The composition of the planetesimals formed at different heliocentric distances, due to the different composition of dust that went on their construction, was different.
It so happened that asteroids are planetesimals formed on the border of hot and cold zones of the protoplanetary disk, which have survived to this day. Although the ring of asteroids has a small length (only about 1 a. u.), the difference in conditions in it was apparently sufficient to form a dissimilar S- and C-asteroids. It is quite logical to think that S-asteroids have formed in a warmer zone, at smaller heliocentric distances than C-asteroids, and now slowly mix. However, since only those bodies that have been formed on the most stable orbits have survived, their complete mixing has not occurred in the past 4.5 billion years.
That is why C-asteroids still gravitate to the outer part of the ring and S-asteroids to the inner part. But when they collide with each other, they contaminate each other's surfaces with their substance, and that's probably why the color of S- and C-asteroids changes slowly with heliocentric distance.
Asteroids were formed in the protoplanetary cloud as loose aggregates. Less gravity could not compress the dusty winters of the planet. Due to the radioactive heat, they were heated up. This heating, as J. Wood's calculations have shown, was very effective: because the loose body is well kept warm. Heating began at the stage of asteroid growth. Their substance in the central parts of the body warmed up, sintering, and maybe even melting, and the dust on the asteroid surface still continued to erupt, replenishing the loose, insulating layer.
The main source of heating is now considered to be aluminum-26, the same aluminum-26, which a million years before the formation of asteroids was injected along with the substance of a supernova into the protosolar nebula.
Collisions of asteroids with each other at the beginning also led to the compaction of their substance. Asteroids became compact bodies. But further disturbances from the growing fallow deer led to an increase in the speed with which the collisions occurred. As a result, more or less compact bodies were broken. The collisions were repeated many times, shaking, stirring, stirring up the debris, and crushing again. That's why modern asteroids are probably poorly packaged lumps.
Small asteroid fragments, of course, come into Earth's orbit from the asteroid ring. This is due to the mechanism of successive resonance orbital swaying under the influence of planetary disturbances, which is not quite clear in detail yet. But the swaying occurs only in some areas of the ring. Asteroids from different places of the ring come in differently effective, and the debris in the vicinity of Earth's orbit may not be representative of those objects that are moving beyond the orbit of Mars.