Embedded in this dust are presolar grains, which predate the formation of our solar system and originated elsewhere in the galaxy.
The chondrules have distinct texture, composition and mineralogy and their origin continues to be the object of some debate.
Chondrites also contain refractory inclusions (including Ca-Al Inclusions), which are among the oldest objects to form in the solar system, particles rich in metallic Fe-Ni and sulfides, and isolated grains of silicate minerals.
The remainder of chondrites consists of fine-grained (micrometre-sized or smaller) dust, which may either be present as the matrix of the rock or may form rims or mantles around individual chondrules and refractory inclusions.
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.
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.
Each chondrite group has a distinctive mixture of chondrules, refractory inclusions, matrix (dust), and other components and a characteristic grain size.
Other ways of classifying chondrites include weathering Chondrites can also be categorized according to their petrologic type, which is the degree to which they were thermally metamorphosed or aqueously altered (they are assigned a number between 1 and 7).
They contain abundant chondrules, sparse matrix (10–15% of the rock), few refractory inclusions, and variable amounts of Fe-Ni metal and troilite (Fe S).
Their chondrules are generally in the range of 0.5 to 1 mm in diameter.
Although chondritic asteroids never became hot enough to melt based upon internal temperatures, many of them reached high enough temperatures that they experienced significant thermal metamorphism in their interiors.