[meteorite-list] iron meteorite cooling rates and Meteorite Men
On last night's Meteorite Men show, the narrator was attempting to explain that the Widmanstatten pattern is caused by kamacite and taenite cooling at different rates. This is incorrect. How could two intergrown metal grains buried deep inside a core cool at different rates? The Widmanstatten pattern forms in the following manner: (1) At high temperatures (but below the solidus), metallic Fe-Ni exists as a single phase -- taenite. (2) As the metal cools, it eventually reaches the two-phase field (or solvus) on the phase diagram. For metal containing 90% iron and 10% nickel, it reaches this boundary when temperatures cool to about 700ºC. (3) At this point, small kamacite grains nucleate inside the taenite. With continued cooling, the kamacite grains grow larger at the expense of taenite, but both phases become richer in nickel. This is possible because the low-Ni phase (kamacite) is becoming increasingly abundant. (4) At low temperatures, say 400ºC or so, diffusion becomes so sluggish that the reaction essentially stops. These meteorites are called octohedrites because solids have three-dimensional structures and the kamacite planes are oriented with respect to each other in the same way as the faces of a regular octahedron. Alan Rubin Institute of Geophysics and Planetary Physics University of California 3845 Slichter Hall 603 Charles Young Dr. E Los Angeles, CA 90095-1567 phone: 310-825-3202 e-mail: aeru...@ucla.edu website: http://cosmochemists.igpp.ucla.edu/Rubin.html __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] iron meteorite cooling rates and Meteorite Men
Thank you Dr. Rubin for that explanation. As a collector of mostly iron meteorites, I've always been fascinated with the various types of etch patterns. My question is, how many years does it take to cool per degree in the vacuum of space? Secondly, what determines the structure from fine to course.is it just the nickel content or does the cooling rate have anything to do with it? Thanks in advance...Arlene - Original Message - From: Alan Rubin aeru...@ucla.edu To: meteorite-list@meteoritecentral.com Sent: Wednesday, December 15, 2010 9:54 AM Subject: [meteorite-list] iron meteorite cooling rates and Meteorite Men On last night's Meteorite Men show, the narrator was attempting to explain that the Widmanstatten pattern is caused by kamacite and taenite cooling at different rates. This is incorrect. How could two intergrown metal grains buried deep inside a core cool at different rates? The Widmanstatten pattern forms in the following manner: (1) At high temperatures (but below the solidus), metallic Fe-Ni exists as a single phase -- taenite. (2) As the metal cools, it eventually reaches the two-phase field (or solvus) on the phase diagram. For metal containing 90% iron and 10% nickel, it reaches this boundary when temperatures cool to about 700ºC. (3) At this point, small kamacite grains nucleate inside the taenite. With continued cooling, the kamacite grains grow larger at the expense of taenite, but both phases become richer in nickel. This is possible because the low-Ni phase (kamacite) is becoming increasingly abundant. (4) At low temperatures, say 400ºC or so, diffusion becomes so sluggish that the reaction essentially stops. These meteorites are called octohedrites because solids have three-dimensional structures and the kamacite planes are oriented with respect to each other in the same way as the faces of a regular octahedron. Alan Rubin Institute of Geophysics and Planetary Physics University of California 3845 Slichter Hall 603 Charles Young Dr. E Los Angeles, CA 90095-1567 phone: 310-825-3202 e-mail: aeru...@ucla.edu website: http://cosmochemists.igpp.ucla.edu/Rubin.html __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] iron meteorite cooling rates and Meteorite Men
If you don't mind my offering a possible answer to this part: what determines the structure from fine to course.I would say it is the width of the kamacite bands. Someone will probably correct me on that though. Mike in CO On Dec 15, 2010, at 11:31 AM, Arlene Schlazer wrote: Thank you Dr. Rubin for that explanation. As a collector of mostly iron meteorites, I've always been fascinated with the various types of etch patterns. My question is, how many years does it take to cool per degree in the vacuum of space? Secondly, what determines the structure from fine to course.is it just the nickel content or does the cooling rate have anything to do with it? Thanks in advance...Arlene - Original Message - From: Alan Rubin aeru...@ucla.edu To: meteorite-list@meteoritecentral.com Sent: Wednesday, December 15, 2010 9:54 AM Subject: [meteorite-list] iron meteorite cooling rates and Meteorite Men On last night's Meteorite Men show, the narrator was attempting to explain that the Widmanstatten pattern is caused by kamacite and taenite cooling at different rates. This is incorrect. How could two intergrown metal grains buried deep inside a core cool at different rates? The Widmanstatten pattern forms in the following manner: (1) At high temperatures (but below the solidus), metallic Fe-Ni exists as a single phase -- taenite. (2) As the metal cools, it eventually reaches the two-phase field (or solvus) on the phase diagram. For metal containing 90% iron and 10% nickel, it reaches this boundary when temperatures cool to about 700ºC. (3) At this point, small kamacite grains nucleate inside the taenite. With continued cooling, the kamacite grains grow larger at the expense of taenite, but both phases become richer in nickel. This is possible because the low-Ni phase (kamacite) is becoming increasingly abundant. (4) At low temperatures, say 400ºC or so, diffusion becomes so sluggish that the reaction essentially stops. These meteorites are called octohedrites because solids have three-dimensional structures and the kamacite planes are oriented with respect to each other in the same way as the faces of a regular octahedron. Alan Rubin Institute of Geophysics and Planetary Physics University of California 3845 Slichter Hall 603 Charles Young Dr. E Los Angeles, CA 90095-1567 phone: 310-825-3202 e-mail: aeru...@ucla.edu website: http://cosmochemists.igpp.ucla.edu/Rubin.html __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] iron meteorite cooling rates and Meteorite Men
I misread your question. Sorry, it is the nickel and cooling rate On Dec 15, 2010, at 11:31 AM, Arlene Schlazer wrote: Thank you Dr. Rubin for that explanation. As a collector of mostly iron meteorites, I've always been fascinated with the various types of etch patterns. My question is, how many years does it take to cool per degree in the vacuum of space? Secondly, what determines the structure from fine to course.is it just the nickel content or does the cooling rate have anything to do with it? Thanks in advance...Arlene - Original Message - From: Alan Rubin aeru...@ucla.edu To: meteorite-list@meteoritecentral.com Sent: Wednesday, December 15, 2010 9:54 AM Subject: [meteorite-list] iron meteorite cooling rates and Meteorite Men On last night's Meteorite Men show, the narrator was attempting to explain that the Widmanstatten pattern is caused by kamacite and taenite cooling at different rates. This is incorrect. How could two intergrown metal grains buried deep inside a core cool at different rates? The Widmanstatten pattern forms in the following manner: (1) At high temperatures (but below the solidus), metallic Fe-Ni exists as a single phase -- taenite. (2) As the metal cools, it eventually reaches the two-phase field (or solvus) on the phase diagram. For metal containing 90% iron and 10% nickel, it reaches this boundary when temperatures cool to about 700ºC. (3) At this point, small kamacite grains nucleate inside the taenite. With continued cooling, the kamacite grains grow larger at the expense of taenite, but both phases become richer in nickel. This is possible because the low-Ni phase (kamacite) is becoming increasingly abundant. (4) At low temperatures, say 400ºC or so, diffusion becomes so sluggish that the reaction essentially stops. These meteorites are called octohedrites because solids have three-dimensional structures and the kamacite planes are oriented with respect to each other in the same way as the faces of a regular octahedron. Alan Rubin Institute of Geophysics and Planetary Physics University of California 3845 Slichter Hall 603 Charles Young Dr. E Los Angeles, CA 90095-1567 phone: 310-825-3202 e-mail: aeru...@ucla.edu website: http://cosmochemists.igpp.ucla.edu/Rubin.html __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] iron meteorite cooling rates and Meteorite Men
Dr. Rubin said ...the narrator was attempting to explain that the Widmanstatten pattern is caused by... And, of course, Dr, Rubin's very succinct correcting explanation is, by the standards of today's media, three paragraphs too long. The time and space requirements of electronic and print media prevent intelligible descriptions of scientific processes. How many times have we seen, or heard, ridiculous and missleading accounts made by reporters and pundits based on their refusal to use sweat equity to get some facts straight? I found this only to true whilst trying to describe the physical reasons for an airplane to have had a stall/spin crash to a reporter for a local television station. The story came out that the plane's motor had stalled and stopped the plane in midair causing it to fall to the ground. I had said nothing of the kind. There was a time when major media employed experts in the sciences, so that what was published had some veracity. Now, restraints in time and money and a what the hell...this stuff is too complicated attitude. leave the public in their ignorance. Happy Holidays to all...and thank you Dr. Rubin. Count Deiro IMCA 3536 -Original Message- From: Alan Rubin aeru...@ucla.edu Sent: Dec 15, 2010 9:54 AM To: meteorite-list@meteoritecentral.com Subject: [meteorite-list] iron meteorite cooling rates and Meteorite Men On last night's Meteorite Men show, the narrator was attempting to explain that the Widmanstatten pattern is caused by kamacite and taenite cooling at different rates. This is incorrect. How could two intergrown metal grains buried deep inside a core cool at different rates? The Widmanstatten pattern forms in the following manner: (1) At high temperatures (but below the solidus), metallic Fe-Ni exists as a single phase -- taenite. (2) As the metal cools, it eventually reaches the two-phase field (or solvus) on the phase diagram. For metal containing 90% iron and 10% nickel, it reaches this boundary when temperatures cool to about 700ºC. (3) At this point, small kamacite grains nucleate inside the taenite. With continued cooling, the kamacite grains grow larger at the expense of taenite, but both phases become richer in nickel. This is possible because the low-Ni phase (kamacite) is becoming increasingly abundant. (4) At low temperatures, say 400ºC or so, diffusion becomes so sluggish that the reaction essentially stops. These meteorites are called octohedrites because solids have three-dimensional structures and the kamacite planes are oriented with respect to each other in the same way as the faces of a regular octahedron. Alan Rubin Institute of Geophysics and Planetary Physics University of California 3845 Slichter Hall 603 Charles Young Dr. E Los Angeles, CA 90095-1567 phone: 310-825-3202 e-mail: aeru...@ucla.edu website: http://cosmochemists.igpp.ucla.edu/Rubin.html __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] iron meteorite cooling rates and Meteorite Men
The iron meteorite cooling rates generally range from about 1 - 100ºC/Myr. The reason for such slow rates is that the metal cores are buried deeply within silicate mantles and heat cannot readily escape. The coarseness of the Widmanstatten pattern is a function of cooling rate -- more slowly cooled irons will develop thicker kamacite lamellae. But there are two other factors that govern the coarseness of the structure -- the Ni concentration and the nucleation temperature. The lower the Ni concentration in the metal, the more kamacite will develop upon cooling. Metal that begins to nucleate at a higher temperature will have a longer period within which kamacite can grow. Alan Rubin Institute of Geophysics and Planetary Physics University of California 3845 Slichter Hall 603 Charles Young Dr. E Los Angeles, CA 90095-1567 phone: 310-825-3202 e-mail: aeru...@ucla.edu website: http://cosmochemists.igpp.ucla.edu/Rubin.html __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] iron meteorite cooling rates and Meteorite Men
Hi List. (ot a chemist, me, just a collector, not ametorologist, just a passionate meteorite guy. This is mostly a question from Allan's post just now: I was always under the impression that iron meteorites resulted from colliding differentiated parent-bodies, and that the crystallization sequence was achieved after an impact that exposed a core, molten NiFe suddenly ejected into space without the shield of its former silicate mantle. Am I way off base? Does Thompson structure develope within? - Original Message - From: Alan Rubin aeru...@ucla.edu To: meteorite-list@meteoritecentral.com Sent: Wednesday, December 15, 2010 4:21 PM Subject: Re: [meteorite-list] iron meteorite cooling rates and Meteorite Men The iron meteorite cooling rates generally range from about 1 - 100ºC/Myr. The reason for such slow rates is that the metal cores are buried deeply within silicate mantles and heat cannot readily escape. The coarseness of the Widmanstatten pattern is a function of cooling rate -- more slowly cooled irons will develop thicker kamacite lamellae. But there are two other factors that govern the coarseness of the structure -- the Ni concentration and the nucleation temperature. The lower the Ni concentration in the metal, the more kamacite will develop upon cooling. Metal that begins to nucleate at a higher temperature will have a longer period within which kamacite can grow. Alan Rubin Institute of Geophysics and Planetary Physics University of California 3845 Slichter Hall 603 Charles Young Dr. E Los Angeles, CA 90095-1567 phone: 310-825-3202 e-mail: aeru...@ucla.edu website: http://cosmochemists.igpp.ucla.edu/Rubin.html __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] iron meteorite cooling rates and Meteorite Men
Magmatic iron meteorites (including the large IIIAB group) are thought to have formed by fractional crystallization within the cores of differentiated asteroids, layered by silicate mantles. Asteroidal collisions can eventually expose the cores (which in many or most cases have already crystallized) and send some of the pieces on their way to the inner solar system. Nonmagmatic irons (such as IAB) are more controversial. Some think that they also formed in cores; others that they formed as metal melt pools at the bottoms of impact craters on chondritic asteroids. Alan Rubin Institute of Geophysics and Planetary Physics University of California 3845 Slichter Hall 603 Charles Young Dr. E Los Angeles, CA 90095-1567 phone: 310-825-3202 e-mail: aeru...@ucla.edu website: http://cosmochemists.igpp.ucla.edu/Rubin.html - Original Message - From: Richard Montgomery rickm...@earthlink.net To: Alan Rubin aeru...@ucla.edu; meteorite-list@meteoritecentral.com Sent: Wednesday, December 15, 2010 4:47 PM Subject: Re: [meteorite-list] iron meteorite cooling rates and Meteorite Men Hi List. (ot a chemist, me, just a collector, not ametorologist, just a passionate meteorite guy. This is mostly a question from Allan's post just now: I was always under the impression that iron meteorites resulted from colliding differentiated parent-bodies, and that the crystallization sequence was achieved after an impact that exposed a core, molten NiFe suddenly ejected into space without the shield of its former silicate mantle. Am I way off base? Does Thompson structure develope within? - Original Message - From: Alan Rubin aeru...@ucla.edu To: meteorite-list@meteoritecentral.com Sent: Wednesday, December 15, 2010 4:21 PM Subject: Re: [meteorite-list] iron meteorite cooling rates and Meteorite Men The iron meteorite cooling rates generally range from about 1 - 100ºC/Myr. The reason for such slow rates is that the metal cores are buried deeply within silicate mantles and heat cannot readily escape. The coarseness of the Widmanstatten pattern is a function of cooling rate -- more slowly cooled irons will develop thicker kamacite lamellae. But there are two other factors that govern the coarseness of the structure -- the Ni concentration and the nucleation temperature. The lower the Ni concentration in the metal, the more kamacite will develop upon cooling. Metal that begins to nucleate at a higher temperature will have a longer period within which kamacite can grow. Alan Rubin Institute of Geophysics and Planetary Physics University of California 3845 Slichter Hall 603 Charles Young Dr. E Los Angeles, CA 90095-1567 phone: 310-825-3202 e-mail: aeru...@ucla.edu website: http://cosmochemists.igpp.ucla.edu/Rubin.html __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
