Composition of the asteroid

(ORDO NEWS) — Meteorites are extremely diverse, as are their parent bodies – asteroids. At the same time, the wretchedness of their mineralogical composition is striking.

Meteorites consist mainly of iron-magnesian silicates – olivines and pyroxenes of various compositions, from almost pure fayalite and ferrosilite, which do not contain magnesium, to almost pure forsterite and enstanite, which do not contain iron.

They are present as small crystals or as glass, usually partially recrystallized. Another main component is nickel iron, which is a solid solution of nickel in iron, and, as in any solution, the nickel content in iron varies from 6-7% to 30-50%. Nickel-free iron is also occasionally found.

Iron sulfides are sometimes present in significant amounts. Other minerals are in small quantities. Only about 150 minerals have been identified, and although even now more and more are being discovered, it is clear that the number of meteorite minerals is very small compared to their abundance in the rocks of the Earth, where more than 1000 of them have been discovered.

This indicates the primitive, undeveloped nature of the meteorite substances. Many minerals are present not in all meteorites, but only in some of them.

The most common meteorites are chondrites. These are stone meteorites from light gray to very dark in color with an amazing structure: they contain rounded grains – chondrules, sometimes clearly visible on the fault surface and easily crumbled from the meteorite.

The sizes of chondrules are different – from microscopic to centimeter. They occupy a significant volume of the meteorite, sometimes up to half of it, and are weakly cemented by an interdchondral matrix. The composition of the matrix is ‚Äč‚Äčidentical with the composition of chondrules, and sometimes differs from it.

Broken chondrules and their fragments are often found in the interchondral substance. Such a structure is inherent only in meteorites (and many of them!) and is not found anywhere else. Composed mainly of iron-magnesian silicates, chondrites also contain fine nickel iron, sulfides and other minerals.

There are many hypotheses regarding the origin of chondrules, but all of them are controversial. In short, the origin of chondrules is still unknown. There are HH, H, L and LL chondrites with very high, low and very low content of free metallic iron.

Accordingly, when moving from one class to another, the total content of iron (free and included in silicates) also decreases.

In addition, there is a group of E-chondrites, in which almost all iron is in a free state, so that 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 silicates.

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