![]() Some mineral fragments show zoning (lightening towards the edge) related to thermal alteration, but it is minimal and not seen in all minerals or chondrules. The light grey matrix consists of fine silicates and clay minerals with finely disseminated iron and sulfide inclusions. A backscattered-electron image of NWA 7892, a CO3.05. That’s 4.557 billion years of cold storage in some cases. Some type 1 and 2 meteorites have *never* been heated above ~150☌ since forming. If the number is less than a 3, the meteorite wasn’t heated/melted, but was instead altered by the presence of water into clay minerals (likely at temperatures at which liquid or frozen water would be stable). Past 6 or 7 (it’s debated as to whether type-7 chondrites are a legitimate thing), you wouldn’t be able to see the chondrules anymore and you would have a ‘primitive achondrite.’ Aka, a melted chondrite, with no visible chondrules. The higher the number (3.0 to 6), the more (re)melted the chondrules get, until you can’t see them anymore. The number following the letter(s) determines the nature and amount of alteration that the meteorite has undergone since its chondrules first solidified.Ī type-3.0 chondrite would be essentially unchanged since forming. The first letter(s) in the classification denote a group of meteorites determined by chemical differences. I might have missed a theory or two, but those are the ones that come to mind.Ĭhondrite nomenclature is pretty easy to understand once you get the hang of it. from a superheated nebula, as it cooled)Ģ) the product of lightning propagating through nebular dustģ) produced by the gravitational or pressure bow-shock waves of planetesimals, orĤ) the product impacts (condensed droplets of rock vaporizes in impacts). Current hypotheses are that chondrules are:ġ) direct condensates (e.g. How the repeating, extraordinarily high temperature events that formed chondrules occurred is still unknown. Yet the matrix surrounding chondrules formed at temperatures closer to 800☌. Figure 1d., from Coarse-grained chondrule rims in type 3 chondrites, by A.E. So, whatever formed them was (sometimes) cyclic or repeating in nature. Some chondrules exhibit concentric layering up to five melting/depositional events have been observed in single chondrules. They are high-temperature droplets of silicate minerals such as olivine, pyroxene, and feldspars they were heated to ~1,500+☌, and then quenched in a matter of minutes. Image courtesy of NASA.Ĭhondrules are enigmatic. An artistic rendition of the early solar nebula, birthplace of the chondrites. They are called chondrites because they contain structures called chondrules: small, spherical droplets of rock that condensed in the solar nebula via still-debated and little-understood processes. They have formation ages dating to at least 4.56 billion years before the present, and have been little changed since then. Chondrites are the most primitive group of meteorites.
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