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.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.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.Chondrites were formed by the accretion of particles of dust and grit present in the primitive Solar System which gave rise to asteroids over 4.55 billion years ago.
R (Rumuruti type) chondrites are a very rare group, with only one documented fall out of almost 900 documented chondrite falls.
The net result of these secondary thermal, aqueous, and shock processes is that only a few known chondrites preserve in pristine form the original dust, chondrules, and inclusions from which they formed.
Prominent among the components present in chondrites are the enigmatic chondrules, millimetre-sized spherical objects that originated as freely floating, molten or partially molten droplets in space; most chondrules are rich in the silicate minerals olivine and pyroxene.
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.