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April 2008
Now Meteorites! Click Here

September 18, 2007
New additions!
New minerals added. See our Minerals section clicking here

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Chondrites

In addition to the silicaceous chondrules, chondrites contain variable amounts of free metal (Fe, Ni).
Chondrites are subdivided into 3 main groups. In order of decreasing degree of oxidation of the iron (Fe) that they contain, these are: carbonaceous chondrites, ordinary chondrites, and enstatite chondrites. 

Within each of these groups, chondrites are also classified according to their petrologic type; that is, on the basis of the degree of alteration (or alteration grade) to which they have been subjected on their parent body prior to arriving on Earth. This degree of alteration ranges from 1 to 6, grade 3 corresponding to the least altered state. The grade decreases from 3 to 1 as aqueous alteration (alteration by liquid water) intensifies, while the grade increases from 3 to 6 as thermal metamorphism (alteration by heating) increases. At grade 6, chondrites have undergone such intense heating and attendant recrystallization that chondrules may be almost completely obliterated. Carbonaceous chondrites have mostly undergone aqueous alteration (none are of grade higher than 4), while most ordinary and enstatite chondrites have undergone thermal metamorphism (none are of grade lower than 3).

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