They are divided into three groups, which have different amounts of metal and different amounts of total iron: Another of their main characteristics is the presence of water or of minerals that have been altered by the presence of water.
There are many groups of carbonaceous chondrites, but most of them are distinguished chemically by enrichments in refractory lithophile elements relative to Si and isotopically by unusually low They are characterized by large amounts of dusty matrix and oxygen isotope compositions similar to carbonaceous chondrites, highly reduced mineral compositions and high metal abundances (6% to 10% by volume) that are most like enstatite chondrites, and concentrations of refractory lithophile elements that are most like ordinary chondrites.
In addition, all chondritic asteroids were affected by impact and shock processes due to collisions with other asteroids.
Ordinary chondrites are distinguished chemically by their depletions in refractory lithophile elements, such as Ca, Al, Ti, and rare earths, relative to Si, and isotopically by their unusually high O compared to Earth rocks.
Most, but not all, ordinary chondrites have experienced significant degrees of metamorphism, having reached temperatures well above 500 °C on the parent asteroids.
The chondrules in a chondrite that is assigned a "3" have not been altered.
Larger numbers indicate an increase in thermal metamorphosis up to a maximum of 7, where the chondrules have been destroyed.
Numbers lower than 3 are given to chondrites whose chondrules have been changed by the presence of water, down to 1, where the chondrules have been obliterated by this alteration.
A synthesis of the various classification schemes is provided in the table below.They are formed when various types of dust and small grains that were present in the early solar system accreted to form primitive asteroids.They are the most common type of meteorite that falls to Earth with estimates for the proportion of the total fall that they represent varying between 85.7% Their study provides important clues for understanding the origin and age of the Solar System, the synthesis of organic compounds, the origin of life or the presence of water on Earth.One of their characteristics is the presence of chondrules, which are round grains formed by distinct minerals, that normally constitute between 20% and 80% of a chondrite by volume.There are currently over 27,000 chondrites in the world's collections.Many chondritic asteroids also contained significant amounts of water, possibly due to the accretion of ice along with rocky material.