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TITLE: Chondrites

[Photo: Magnified Space Dust]

When the Solar System was still just a rotating disk of gas and dust, the gentle clumping together of dust particles began the process that ultimately created the planets: accretion. Chondrite meteorites are actual mixtures of this 4.6-billion-year-old dust! When these rocks land on Earth, they give us an invaluable look at how the accretion process worked so long ago.

About 85 percent of the meteorites that fall to Earth are chondrites. Three major varieties have been recognized, and each has several subcategories distinguished by chemical composition.

See caption at right.

Carbonaceous Chondrites
Despite their name, not all the carbonaceous chondrites are rich in carbon. Many contain abundant water. Some even possess complex organic molecules like amino acids, albeit of nonbiologic origin.


See caption at right.

Enstatite Chondrites
The abundance of metal flakes in these specimens is the hallmark of enstatite chondrites. Their iron is metal or sulfide—none is combined with oxygen, showing that they formed in an oxygen-poor environment. Later impacts produced Abee's fragmented texture.


See caption at right.

Ordinary Chondrites
The most common meteorites, ordinary chondrites come from just three parent asteroids represented by these three specimens. The different abundances of shiny metal flakes show that the three stones have different chemical compositions.

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Smithsonian National Museum of Natural History Department of Mineral Sciences website Credits