Re: [meteorite-list] Irons and fusion crusts
--- Gary K. Foote [EMAIL PROTECTED] wrote: Hi Phil, I don't mean to split hairs, but what is the difference between a thermal alteration zone and a fusion crust? Is there a difference? Is not a fusion crust a thermal alteration zone? Gary Oh, no, no, no. A fusion crust is formed by the melting of the very outer layer, proper actual melting. Thermal alteration is caused by the presence of heat without actually causing melting. The best I can think of as an example is car brake disks when they get too hot. When they cool back down they have a blue tint. This is thermal alteration and exists to some depth in the disk, not just on the surface. This is important because it's not actually melted, it's just the heat has alterd the crystal structure. RMcC Sucker-punch spam with award-winning protection. Try the free Yahoo! Mail Beta. http://advision.webevents.yahoo.com/mailbeta/features_spam.html __ Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
[meteorite-list] Irons and fusion crusts
I know this has been a debate that has ebbed and flowed across this list many times. I want to point everyone to this fabulous picture of Thunda - a Queensland iron that clearly shows a crust of differentiated iron surrounding a 'typical' iron core. This, in my mind, is a stupendous example of an iron meteorite with a fantastic fusion crust. http://www.rawnet.com.au/~qwalkra1/thunda.htm My thanks to Bob Walker for bringing this to the public eye. Gary http://www.meteorite-dealers.com __ Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Irons and fusion crusts
Hi Phil, I don't mean to split hairs, but what is the difference between a thermal alteration zone and a fusion crust? Is there a difference? Is not a fusion crust a thermal alteration zone? Gary On 15 Jan 2007 at 19:07, Phil Morgan wrote: I think we're seeing a thermal alteration zone rather than anything that could be called a fusion crust. __ Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Irons and fusion crusts
Hi Gary, Nice discussion! I think there is a big difference between fusion crust for irons and just a thermally altered zone. Fusion requires the crust to have been fused. At velocities over 3 km/s the fusing material is the same material that is ablating, and as we know very little remains stuck in flight. (However a great amount can flow - just look at aerodynamically sculpted iron meteorites!) After slowing or stopping some of the ablation melt is left and solidifies. Thermal alteration has never flowed to these high degrees and that is how I'd split hairs; some level of structure is maintained at some levels - unlike the ablativly free flowing fusion crust. A while back when David Weir and I participated in this conservation, and David posted a nice cross-section of a typical iron meteorite fusion crust. You can search the archives for the link if you don't have it. It was maybe two months ago? Best health, Doug - Original Message - From: Gary K. Foote [EMAIL PROTECTED] To: Phil Morgan [EMAIL PROTECTED]; meteorite-list@meteoritecentral.com Sent: Monday, January 15, 2007 8:11 PM Subject: Re: [meteorite-list] Irons and fusion crusts Hi Phil, I don't mean to split hairs, but what is the difference between a thermal alteration zone and a fusion crust? Is there a difference? Is not a fusion crust a thermal alteration zone? Gary On 15 Jan 2007 at 19:07, Phil Morgan wrote: I think we're seeing a thermal alteration zone rather than anything that could be called a fusion crust. __ Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list __ Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
