Steve Schoner sent a great reply to my iron questions, but forgot to address it to the whole List. He's asked me to forward it so that everyone can read it. Rob. In a message dated 31/03/99 14:17:47 GMT, ams000@aztec.asu.edu writes: << Buchwald in his three volumes _Iron Meteorites_ covers this process fairly well. It has a lot to do with the structure of the meteorite, and how the oxidation process goes along the crystal planes of the kamacite and taenite. There is an ionic proceess involved as well where the electrical charges of the iron atoms and nickel atoms play a part. I am a bit fuzzy on that process, but Buchwald discusses it in lenght. I think that the finer the structure the more resistant is the iron to rusting. But there might be other factors as well, such as fine shock lines and cracks. Any of these can be avenues for oxidation. But it is very interesting how irons and some pallasites oxidize. Huckitta though mostly oxidized shows its olivine structure, and one completely oxidized iron found in Coldwater (?) KS, Nininger discovered that upon cutting that the widmanstatten pattern was still evident. Irons will all eventually rust away, and how fast that process occurs depends on enviromental conditions. How long that process takes is I think a matter of speculation. In the case of the largest iron meteorite known Hoba, there is at least a foot of iron shale beneath it. I have heard estimates that it may have fallen at least 500,000 years ago. Eventually though, after millions of years all of it will be rusted, and leached, then washed as iron ions into the sea, and then re-combine with other elements to form the more mundane iron mineral deposites found all over the earth's surface. And how much of the iron that cyano-bacteria extract from the ocean waters came from meteorites only one can guess. Steve Schoner AMS >>
-- BEGIN included message
- To: FERNLEA4@AOL.COM
- Subject: Re: Question about irons
- From: ams000@aztec.asu.edu (STEVEN R. SCHONER)
- Date: Wed, 31 Mar 1999 07:16:28 -0700 (MST)
- Reply-to: ams000@aztec.asu.edu
> >Hi all, > >Does anyone want to buy any toner?.........(just kidding!) > >Can anyone explain why so many ancient iron finds seem to oxidise in different >ways? For example, some iron finds seem to consist of nothing but heavily >oxidised balls of flaking shale, while others have oxidised into solid >hematite. >I know that Earth age & environmental conditions play a major role, but what's >the key that determines if the iron completely rusts through into the shale >and/or hematite forms? Also, is hematite the end of the line, or will this >degrade/oxidise further in time? > >So many questions!....thanks in advance. > Buchwald in his three volumes _Iron Meteorites_ covers this process fairly well. It has a lot to do with the structure of the meteorite, and how the oxidation process goes along the crystal planes of the kamacite and taenite. There is an ionic proceess involved as well where the electrical charges of the iron atoms and nickel atoms play a part. I am a bit fuzzy on that process, but Buchwald discusses it in lenght. I think that the finer the structure the more resistant is the iron to rusting. But there might be other factors as well, such as fine shock lines and cracks. Any of these can be avenues for oxidation. But it is very interesting how irons and some pallasites oxidize. Huckitta though mostly oxidized shows its olivine structure, and one completely oxidized iron found in Coldwater (?) KS, Nininger discovered that upon cutting that the widmanstatten pattern was still evident. Irons will all eventually rust away, and how fast that process occurs depends on enviromental conditions. How long that process takes is I think a matter of speculation. In the case of the largest iron meteorite known Hoba, there is at least a foot of iron shale beneath it. I have heard estimates that it may have fallen at least 500,000 years ago. Eventually though, after millions of years all of it will be rusted, and leached, then washed as iron ions into the sea, and then re-combine with other elements to form the more mundane iron mineral deposites found all over the earth's surface. And how much of the iron that cyano-bacteria extract from the ocean waters came from meteorites only one can guess. Steve Schoner AMS >Best wishes, >Rob Elliott. >http://hometown.aol.com/fernlea4/forsale.html >Fernlea Meteorites, >Milton of Balgonie, Fife. KY7 6PY >Scotland. UK. >Tel: +44-(0)1592-751563 >Fax: +44-(0)1592-751060 >Email: FERNLEA4@aol.com > >---------- >Archives located at: >http://www.meteoritecentral.com/list_best.html > >For help, FAQ's and sub. info. visit: >http://www.meteoritecentral.com/mailing_list.html >---------- > > >
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