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Comets are mostly icy but they should have some rocky components too, right? I wonder if there's any rocky piece of a former comet among collected meteorites. Is it possible today to identify a meteorite as having cometary origin? Or has surviving pieces from comet impacts been too rare (or violent vapourizing) events?

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This page -- http://www.amsmeteors.org/fireballs/faqf/ -- suggests that it's very unlikely to find cometary-origin meteorites, even though the majority of observed meteors are cometary in origin, because the latter are too fragile to survive all the way to the ground:

Based upon photographic fireball studies, cometary meteoroids have extremely low densities, about 0.8 grams/cc for class IIIA fireballs, and 0.3 grams/cc for class IIIB fireballs. This composition is very fragile and vaporizes so readily when entering the atmosphere, that it is called “friable” material. These meteoroids have virtually no chance of making it to the ground unless an extremely large piece of the comet enters the atmosphere, in which case it would very likely explode at some point in its flight, due to mechanical and thermal stresses.

It goes on to claim that cometary meteoroids make up about 95% of observed meteors, 38% of observed fireballs, and 0% of fresh meteorites. (Since a hypothetical cometary-origin meteorite would weather faster than meteorites of asteroidal origin, they would be even less likely to be found later, and so it's not surprising that the page says 0% of all known meteorites are of cometary origin.)

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  • $\begingroup$ I read somewhere that about 50,000 meteorites have been collected and identified as meteorites. But really not even one comes from a comet? So the comets breaking up doesn't change the (vaporising) speed of the fragments alot, I suppose. Tells us they are all fluffy. $\endgroup$
    – LocalFluff
    Jul 2, 2015 at 13:38
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    $\begingroup$ I doubt it's possible to completely rule out the odd cometary-origin meteorite here or there. But it seems that no one has positively identified one yet, and the combination of vaporization in the atmosphere plus weathering on the ground means they'd be very rare. $\endgroup$ Jul 2, 2015 at 13:41
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Well to quote the wikipedia page on the Leonids: "The Leonids are a prolific meteor shower associated with the comet Tempel-Tuttle."

So if a meteorite falls to Earth during the Leonids, it may have originated in Comet Tempel-Tuttle.

Unfortunately, there appears to be no conclusive evidence that any particular meteorite came from any particular Comet. The problem is that we do not have direct samples of cometary material to compare against. See for example Swindles & Campin 2004, though somebody may know of something more recent?

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This is a topic under active debate by the field. M. Gounelle in particular has multiple works published giving various criteria/levels for comet meteorites. K. Lodders also has one, perhaps two papers.

“Comets are mostly icy but they should have some rocky components too, right?”

No, they’re NOT mostly icy. Comas and tails are largely hydrous, because volatiles escape. The comet per se (nucleus) is only minority volatiles, which is how it stays- stays behind, stays a nucleus, stays around long enough to complete at least one orbit and be considered a Solar System body. Examination of 67P/Churyumov-Gerasimenko, followed by Arrokoth, seems to confirm ground experiments with particles and their accretion. A chunk of ice will not ‘stick’ well enough to a second chunk of ice. Rock, to a surprising degree, is necessary to make a body hold; formation of a mostly-icy body during the early Solar System may not even have been possible.

Miura, H., Nakamura, E., and Kunihiro, T. 2022 claim our Ryugu samples are comet samples (Ryugu looks like an extinct comet), but plenty of us debate that one:

The Asteroid 162173 Ryugu: a Cometary Origin, The Astrophysical Journal Letters, v. 925 p. L15

And, if you want to get into decimal places, Yurimoto, Zolensky, and others report that the fluid inclusions of Zag/Monahans are comet brines. The Deuterium/Hydrogen ratio (D/H) of the water is clearly an outer Solar System D/H, while Zag and Monahans are inner Solar System. Therefore, they argue, the two meteorites were cross-contaminated by comets.

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