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Author Topic:   Origin of Asteroids
Minnemooseus
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Posts: 3941
From: Duluth, Minnesota, U.S. (West end of Lake Superior)
Joined: 11-11-2001
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Message 5 of 36 (266118)
12-06-2005 3:23 PM
Reply to: Message 1 by doctrbill
12-06-2005 1:24 PM


Melting point of Quartz
Q. Does Quartz melt at 1300 degrees Fahrenheit?
SiO2 has many different crystal structures, which are stable or metastable at various ranges of temperatures and pressures.
Per An Introduction to the Rock Forming Minerals by Deer, Howie, & Zussman, the ultimate melting point of SiO2 is 1730o Celsius, which (if I did the conversions correctly) equals 3115o Fahrenheit.
Now, I believe the above is for pure SiO2. The presence of water effects the crystallization temperatures. Offhand, I think this is getting into a hybrid area that also involves solution effects.
1300o Fahrenheit equals 690o Celsius. Offhand, this seems to be in the ballpark of the temperature that the last Quartz will crystallize out, when in a cooling high water environment. Once again, this is more a matter of crystallizing out of an water solution, rather that crystallizing out of a melt.
Or something like that.
Moose
Edited to repair coding, which I lost when I did a non-raw text copy and paste.
This message has been edited by minnemooseus, 12-06-2005 03:32 PM

This message is a reply to:
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Minnemooseus
Member
Posts: 3941
From: Duluth, Minnesota, U.S. (West end of Lake Superior)
Joined: 11-11-2001
Member Rating: 10.0


Message 10 of 36 (266131)
12-06-2005 4:21 PM
Reply to: Message 9 by doctrbill
12-06-2005 3:53 PM


Re: Melting point of Quartz
The lowest temperature Quartz crystallization scenario is how pegmatites are formed. These are the VERY coarse grained rocks that might be found as the final phase of a granite bodies formation. I don't know if there are any examples of the reverse process having happened.
Obviously, the final pegmatite crystallization is happening at something greater than standard atmospheric pressures, as the boiling point of water is at or above that c. 700o Celcius temperature.
In all, Walt Brown seems to be, at best, working in the realm of dubious quality science fiction.
Moose

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 Message 9 by doctrbill, posted 12-06-2005 3:53 PM doctrbill has not replied

  
Minnemooseus
Member
Posts: 3941
From: Duluth, Minnesota, U.S. (West end of Lake Superior)
Joined: 11-11-2001
Member Rating: 10.0


(1)
Message 24 of 36 (271486)
12-21-2005 3:42 PM
Reply to: Message 5 by Minnemooseus
12-06-2005 3:23 PM


Re: Melting point of Quartz - trivia addendum
minnemooseus writes:
Per An Introduction to the Rock Forming Minerals by Deer, Howie, & Zussman, the ultimate melting point of SiO2 is 1730o Celsius, which (if I did the conversions correctly) equals 3115o Fahrenheit.
That 1730 Celsius number was for a high pressure crystal form of SiO2 (Beta-Cristobalite). My guess is that temperature was such at much higher than atmospheric pressure. The previous mention of 1600 Celsius may well be correct for SiO2 at atmospheric pressure.
I tried and failed to find a good online silica temperature/presure phase diagram. If one wishes to venture into some highly technical material, you can look at http://arxiv.org/PS_cache/cond-mat/pdf/0406/0406192.pdf.
One also may find some amusement in consulting this Scirus.com search, for "silica phase diagram". That is where I came up with the previous link.
Moose

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