What Is a Chondrite?

Stone meteorites with unique spherulitic structure become chondrites; except for H, He and other volatile components, their chemical composition is closest to that of the sun. Chondrites often contain a large number of millimeter-sized pellets. However, the term chondrite can be applied to any meteorite with a composition close to the sun. Although type I carbonaceous chondrites are not classified as chondrites, they are also classified as chondrites. ^[1]

Chondrites are mainly composed of four components, namely: pellets, Fe-Ni metal calcium-aluminum-rich refractory inclusions (Ca-Al-rich inclusions (CAIs)) and amoeba-like olivine aggregates ( amoeboid olivine aggregates (AOAs) and fine-grained matrix. Generally, scholars believe that spherules, metals and refractory inclusions are formed by high temperature (condensation, evaporation) in the solar nebula. Subsequently, many CAIs, most spherules and Fe-Ni metals were heated during their multi-stage heating. After melting, metals in the matrix, some CAIs, and some chondrites (CH and CB chondrites) appear to have escaped these hot nebula events, although most chondrites have experienced overheating events on their parent asteroids (water Alteration, thermal deterioration and

Chondrites are characterized by chondrites. Most of the pellets are spherical or quasi-spherical, mainly composed of

The petrological classification of chondrites reflects the process of meteorites formation and the changes experienced after formation. According to mineralogy and petrology, chondrites can be divided into 7 types of rocks, representing 7 different degrees of metamorphism. The higher the rock type, the more experienced

The study of chondrites is of great significance. First, the composition of chondrites is consistent with the composition of the solar spectrum, and it is completely different from the surface of the earth and non-chondrites, so it may represent the composition of the primitive sun. Second, the chondrites The age of formation of meteorites (4.6Ga) is older than any of the rocks of the Earth and the Moon, providing a basis for the comparison of the ages of the Moon, the Earth, and the Sun. Third, its petrological characteristics are obviously inconsistent with any known planetary process. The "petrological type" of chondrites is also a widely used parameter to indicate the degree of thermal metamorphism. In the study of meteorites and their parent asteroids, they usually indicate the enclosed temperature or the peak temperature. Chondrites are composed of metal particles (Fe, Ni alloys), meteorite (FeS), and silicates in the form of matrix and pellets: pellets are aggregated from millimeter-sized silicates and are forming meteorites Existed before. This mixture of different materials and microstructure is obviously not the product of the nebula process, but a form of cosmic deposition. Pellet is the main component of most chondrite groups, and it accounts for about 70% to 75% of the volume ratio of undegraded ordinary spherules. Its cause is not clear. It is generally believed that the moment when the spherules formed in the solar nebula Melting is also thought to be due to other causes such as agglomeration. Studies on the composition of spherules can also provide information on nebula heating events. ^[4]