A type of stony meteorite made mostly of iron- and magnesium-bearing silicate minerals that have remained little changed from the dawn of the Solar System, over 4.5 billion years ago. Chondrites are the most common kind of meteorite, accounting for about 86% of falls, and, because they come from asteroids that never melted or underwent differentiation, have, except for the lightest elements, hydrogen and helium, the same elemental composition as the original solar nebula. Chondrites are so named because they nearly all contain chondrules -- little round droplets of olivine and pyroxene that apparently condensed and crystallized in the solar nebula and then accreted with other material to form a matrix.

The variation in chemical composition among chondrites reflects the fact that their parent bodies formed in different regions of the solar nebula and were further subjected to different thermal and chemical processes as well as to impacts with other asteroids. The main groups are H, L, and LL, known collectively as ordinary chondrites, E, known as enstatites, and C, known as carbonaceous chondrites. Other, rarer groups, include the rumurutiites (group R), the kakangariites (group K), and the forsterites (group F). Each group is further subdivided into petrologic types 1 to 7. Types 1 and 2, which are represented only by carbonaceous chondrites, show evidence of having been chemically altered by water to the extent that chondrites are either absent (type 1) or rare (type 2). Petrologic types 3 to 7 have been exposed to varying degrees of thermal metamorphism, reflected in an alteration of the chondrules. Type 3 shows plentiful, unaltered and distinct chondrules, while the chondrules of types 4 to 6 are increasingly indistinct due to heat-caused chemical changes and recrystallization. Type 7 chondrites, in which chondrules are absent, are transitional between chondrites and primitive achondrites. A type of stony meteorite which (usually) contains chondrules.

Ordinary Chondrites

A chondrite that is composed mostly of olivine, orthopyroxene, and a certain percentage of more or less oxidized nickel-iron. Based on the differing content of metal and differing mineralogical compositions, the ordinary chondrites are divided into three distinct groups.
H Group chondrites have a high content of free nickel-iron (15 to 19%) and are attracted easily to a magnet. Their main minerals are olivine and the orthopyroxene bronzite, earning them their older name of bronzite chondrites. Comparison of the reflectance spectra of the H chondrites to the spectra of several main belt asteroids has yielded a probable parent body in the asteroid (6) Hebe. However, Hebe might not be the direct source of the H chondrites; most likely, Hebe collided with another asteroid at some point in his history and larger parts of it were dislodged into an elliptical near-earth orbit, from which fragments eventually came to Earth.

L Group chondrites are low in free nickel-iron (4 to 10%) and also contain olivine and the orthopyroxene hypersthene. The asteroid (433) Eros is suspected as a parent body, based on reflectance spectra, but most L chondrites show signs of severe shock metamorphism suggesting a violent history of the parent. Possibly the L chondrites came from a relative or a former part of Eros that was entirely broken up when it collided with another asteroid.

LL Group chondrites ("low iron"/"low metal") have only 1 to 3% free metal. Their olivine is more iron-rich than in the other ordinary chondrites, implying that the LL types must have formed under more oxidizing conditions than their H or L cousins. Scientists are still searching for a probable parent body for this group. One small main belt asteroid, (3628) Boznemcová, shows a similar reflectance spectrum, but with a diameter of just 7 km it seems too small to be regarded as the progenitor of the LL members.

Enstatites

The rarest of the three main types of chondrite, accounting for about 1.5% of falls in this category of meteorite. The name derives from the most abundant mineral present, a pyroxene known as enstatite, Mg₂Si₂O₆. Whereas virtually all pyroxenes found on Earth, the Moon, and in other meteorites contain both magnesium (Mg) and iron (Fe), enstatite is almost iron-free. The iron found in enstatite chondrites, which accounts for 15 to 25% of their mass, is in a metallic state. Stranger still, many elements that normally reside in silicate (rocky) minerals are found instead in sulfide minerals with the result that enstatites contain a wide assortment of uncommon sulfides. Even the metallic iron has up to several percent of silicon. Moving silicon to metallic iron requires a very reducing, oxygen-depleted environment. Some researchers believe the parent body may be an asteroid inside the orbit of Venus or even Mercury (see vulcanoid), while others suggest that a formation in the inner part of the main asteroid belt would have provided the same conditions in the early Solar System. Enstatite chondrites are similar to ordinary chondrites and have been further subdivided based on their content of total iron: members of the EL group contain less iron than members of the EH group. Despite these differences, most researchers believe that both subgroups originated on the same asteroid, most probably representing different layers of the parent body. A comparison of the reflectance spectra of different asteroids to the spectrum of the EH chondrite Abee suggests that the main belt asteroid (16) Psyche may be the common parent for the enstatite chondrites.

Carbonaceous Chondrite

A rare type of stony meteorite which contains large amounts of the magnesium-rich minerals olivine and serpentine and a variety of organic compounds, including amino acids. Although fewer than 100 carbonaceous chondrites are known, they provide a great deal of information about the origin of the Sun and planets, and even of life itself (see organic matter, in meteorites).

Carbonaceous chondrites are the most primitive and unaltered type of meteorite known, with an elemental composition probably similar to that of the nebula from which the Solar System formed. In addition to silicates, oxides, and sulfides, they contain, most distinctively, water or minerals that have been altered in the presence of water, together with large amounts of carbon, including organic compounds. The most pristine carbonaceous chondrites have never been heated above 50°C. Different groups of carbonaceous chondrites have been identified that came from parent bodies in different parts of the solar nebula.

Rumurutites

A member of a rare group of chondrites, formerly known as the Carlisle Lakes group, for a meteorite that was found in Australia in 1977. It is now named for the type specimen Rumuruti that fell in Kenya, Africa, in 1934. Rumuruti is the only witnessed fall of this group and only one small individual has been preserved in the collection of the Humboldt Museum Berlin, Germany, since 1938. It was thought to be an anomalous chondrite until it was reclassified in 1993 and the R group was formed. The R chondrites are quite different from ordinary chondrites and are the opposite of the E chondrites when it comes to mineralogy and their state of oxidation. The members of this group are highly oxidized, containing high amounts of iron-rich olivine. There is practically no free metal inside the R chondrites since most of the iron is either oxidized or found in the form of iron sulfides. The iron-rich olivines, along with the oxidized nature of the iron, give most R chondrites a typical red appearance. The meteorites of this group contain fewer chondrules than do ordinary chondrites or enstatite chondrites, but they often contain xenolithic inclusions that indicate a regolith origin, representing samples of the surface of an asteroid. Another indicator for a regolith origin is the fact that most members of the R group contain high amounts of noble gases implanted into the rock by the solar wind. The parent body of the R chondrites has yet to be found, but it must have been subjected to many impact events during its history to result in the high degree of brecciation that most R group members show.

Kakangarites

A member of a rare group of chondrites, group K, named for their type specimen, the Kakangari meteorite that fell in Tamil Nadu, India, in 1890. Only three specimens are known with a total mass of less than 0.4 kg, all of which are rich in the iron sulfide, troilite, and show numerous primitive, armored chondrules. Unique in their chemical composition and with an oxygen-isotopic signature that distinguishes them from all other chondrites, K chondrites are thought to have originated in a small, primitive parent body that has yet to be identified.

Forsterites

A member of a rare group (also known as the F group) of chondrite meteorites, named for the presence in them of the magnesium-rich type of olivine known as forsterite. In terms of their chemical and mineralogical makeup, forsterites are intermediate between the H group of ordinary chondrites and the E chondrites. They are thought to have derived from a small and primitive asteroid of F chondritic composition that collided with the aubrite parent body shortly after their formation in the early Solar System.