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Dry Ice
  
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Tom Mazanec




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PostPosted: Dec 19, 2016 18:23    Post subject: Dry Ice  

Since inner Antarctic temperatures in winter nights can reach dry ice temperatures, would carbon dioxide be a mineral there?
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Bob Harman




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PostPosted: Dec 19, 2016 19:03    Post subject: Re: Dry Ice  

An interesting question. In the coldest part of the long Antarctic winter night (about -100 F or more) can ambient air molecules containing carbon dioxide sublime out as flakes of solid carbon dioxide?

I am no expert, but theoretically I suppose maybe, but practically speaking no. Even at the Antarctic's extreme low temperatures, there just is not enough CO2 naturally occurring in the air to allow NATURAL crystallization.

Unlike water ice, I believe all dry ice on Earth is man manufactured rather than natural and would therefore not be considered a naturally occurring mineral. But, hey, that is my opinion and maybe I am wrong. BOB
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Cesar M. Salvan
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PostPosted: Dec 19, 2016 19:08    Post subject: Re: Dry Ice  

To the best of my knowledge, there is no naturally occurring solid carbon dioxide (dry ice) on Earth.

CO2 is a trace gas. Its importance could give the impression to the public that its concentration is high, but actually is, in chemical terms, low enough to avoid the formation of solid CO2, which is not possible even at the lower temperatures in Antarctica. If formed (artificially), it readily sublimates. At the high pressures of sea bottom, assuming that the temperature is low enough, is possible the stable existence of solid CO2, but, again, the concentration is too low.

In Mars, at temperatures way lower than minimum temperatures on Earth, there are temporary accumulations of dry ice. In my opinion it could be regarded as a mineral, in the same way water ice is. Mars and other places (Titan for example) will provide us some new minerals. But, for now, dry ice is not a mineral and will not be a mineral in the near future.

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Roger Warin




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PostPosted: Dec 20, 2016 15:19    Post subject: Re: Dry Ice  

Yes you are right.
Water and CO2 are "minerals". Organic chemistry is carbon chemistry. And carbon must have all the potential subtleties it possesses. Carbon dioxide is a mineral, as carbon itself.
But in the case of asteroids and planets deprived of oxygen, the main difference lies in the existence of unstable molecules on Earth (because of oxygen), such as phosphides (schreibersite: Ferro-nickel phosphide) or even native metals as iron (unknown on Earth except at the heart of certain deposits). Otherwise chemistry (and mineralogy) is the same everywhere if external conditions permit.
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alfredo
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PostPosted: Dec 21, 2016 02:47    Post subject: Re: Dry Ice  

Liquid carbon dioxide exists on Earth as microinclusion "bubbles" inside some crystals of quartz, topaz, beryl... I suspect that liquid CO2 bubbles might be responsible for the occasional violent explosions of Pakistani aquamarine crystals in hot display cases. It just doesn't get cold enough for the liquid CO2 to freeze.

In order for the IMA to formally accept "dry ice" as a mineral species, it is not sufficient to just have theoretical evidence for its existence. There are procedures.... You have to find an actual specimen in Nature, move it to a laboratory, keep it cold enough to x-ray it and measure its optical properties, submit the description to the IMA new minerals commission, send the type specimen for preservation to an appropriate institution...Might not be done anytime soon, although similar difficulties were overcome to describe ernstburkeite recently.

Actually one doesn't need to go all the way to Mars to find super-cold minerals that aren't officially described yet. There are far more abundant minerals that are not yet on our "official" species lists due to the extra trouble required to study unstable cold stuff - Like the billions of tons of "methane hydrate' on Earth.
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