[meteorite-list] Red(dish) Fusion Crust
Hello All, And the red crust isn't just found on trailing faces of stones: http://www.ebay.com/itm/meteorite-Chelyabinsk-chondrite-LL5-complete-stone-14-65-g-recent-fall-Russia-/161029553312?pt=LH_DefaultDomain_0hash=item257e1bfca0nma=truesi=jHrsL50utK2qqpfbNFqr9%252BcmQSM%253Dorig_cvip=truert=nc_trksid=p2047675.l2557 It's been seen on stones from just about every reasonably-sized L and LL multiple-stone fall I can think of, and has been discussed on the list as far back as 2007, if not earlier. Similar stones have been noted from Breja, Bensour, Battle Mountain, Ash Creek, Mifflin, etc. This list seems to have a short memory. For those who are curious, magnetite content is a bit vague. The difference in fusion crust coloration is most likely caused by the oxidative state of the iron in the fusion crust. http://en.wikipedia.org/wiki/Iron_oxide If we assume that water is not abundant in the fusion crust due to the high heat necessary to form a fusion crust (perhaps wrong, but simplifies things), we have three oxides to work with: -- From above: Wüstite (FeO) is a mineral form of iron (II) oxide found with meteorites and native iron. *It has a gray color with a greenish tint in reflected light.* Magnetite is a mineral, one of the two common naturally occurring iron oxides (chemical formula Fe3O4). Magnetite has been very important in understanding the conditions under which rocks form. Magnetite reacts with oxygen to produce hematite, and the mineral pair forms a buffer that can control oxygen fugacity. *Generally black or silvery, can have a brownish tint.* Iron (III) oxide or ferric oxide is the inorganic compound with the formula Fe2O3. We'd most likely be dealing with alpha-phase ferric oxide because it is the most stable Fe2O3 phase over ~500°C. This one's also called hematite. *Fe2O3 is dark red.* -- The wikipedia page above links to nice summaries of the hydrous oxides as well, if you want to check them out. The variables we have to work with are: the amount of iron in the meteorite, plus abundances of other minerals that could affect oxide or other mineral formation in the crust. Fragment shape and orientation probably control oxygen flow to given areas (see link below) but also -- ...the entry speed/angle and breakup height would probably help to determine the rate of ablation/deceleration of given fragments (e.g. the point at which fusion crust will remain on the surface of the meteorite versus ablating away), which would also affect the temperature at which the remaining fusion crust formed (a potential variable controlling the oxidative state of iron?). Either way, since access to oxygen seems to determine the redness of the fusion crust, altitude of fragmentation is probably quite important. http://www.ebay.com/itm/Chelyabinsk-Meteorite-Fall-from-Feb-15th-2013-in-Russia-7-098-grams-/111073775576?pt=LH_DefaultDomain_0hash=item19dc834fd8 ^One of the better examples currently on ebay, with topographically low areas that clearly show reddening/browning. In short, yes, hematite is red, so hematite content is a good candidate for the 'reddening agent.' But, then...why don't H chondrites usually form such red fusion crusts? It might be due to the higher iron content in H-chondrites and the ratio of iron to oxygen in the above three oxides. Fe2O3 (hematite) has the lowest Fe to O ratio of the above three minerals (1:1 vs. 3:4 vs. 2:3), so a meteorite that is higher in iron might be less likely to form a lower-iron oxide (hematite) in the same conditions. But this seems somewhat unlikely, as this hypothesized cutoff for hematite formation in the crust would depend on the difference in the modal abundance of Fe in L's versus H's, and that's not a clear boundary. One would have to look at the metal content of various larger multiple falls and examine large numbers of pristine stones from each in order to reach a well-supported answer to that question. Chelyabinsk does support this general hypothesis, though. It broke up at a lower altitude than most bolides do, so fragments should have been exposed to a thicker atmosphere/more oxygen in their final ablative stages of flight. Because of this, we'd expect to see more iron oxides with higher ratios of oxygen to iron in the fusion crust (e.g. our red hematite) . Lo and behold, we're seeing more stones with reddish fusion crusts than usual. This could be a coincidence, but...perhaps not. One should also note that many Chelyabinsks aren't just black or reddish. Many are an unusual lighter brown/grey color: http://www.ebay.com/itm/meteorite-Chelyabinsk-chondrite-LL5-complete-stone-13-14-g-recent-fall-Russia-/161034404036?pt=LH_DefaultDomain_0hash=item257e6600c4 That's a color I've never seen before on an OC, but many Chelyabinsks show it. Could higher levels of (grey/metallic) magnetite be the cause? I wonder...and if that's the case, I'd be curious to know why this is specifically happening with Chelyabinsk
Re: [meteorite-list] Red(dish) Fusion Crust
This is seen on many stones, I have a Bensour that is almost red. I have many Chelyabinsk stones also with brown to red crust, and some iridescent in every color in the rainbow. This is seen in many L and LL falls, but generally only before exposure to water. However I found my first Chelyabinsk which was 503 grams, perfect pyramid with one red crusted side, all other sides extremely black. Michael Farmer Sent from my iPad On May 29, 2013, at 8:00 AM, Jason Utas meteorite...@gmail.com wrote: Hello All, And the red crust isn't just found on trailing faces of stones: http://www.ebay.com/itm/meteorite-Chelyabinsk-chondrite-LL5-complete-stone-14-65-g-recent-fall-Russia-/161029553312?pt=LH_DefaultDomain_0hash=item257e1bfca0nma=truesi=jHrsL50utK2qqpfbNFqr9%252BcmQSM%253Dorig_cvip=truert=nc_trksid=p2047675.l2557 It's been seen on stones from just about every reasonably-sized L and LL multiple-stone fall I can think of, and has been discussed on the list as far back as 2007, if not earlier. Similar stones have been noted from Breja, Bensour, Battle Mountain, Ash Creek, Mifflin, etc. This list seems to have a short memory. For those who are curious, magnetite content is a bit vague. The difference in fusion crust coloration is most likely caused by the oxidative state of the iron in the fusion crust. http://en.wikipedia.org/wiki/Iron_oxide If we assume that water is not abundant in the fusion crust due to the high heat necessary to form a fusion crust (perhaps wrong, but simplifies things), we have three oxides to work with: -- From above: Wüstite (FeO) is a mineral form of iron (II) oxide found with meteorites and native iron. *It has a gray color with a greenish tint in reflected light.* Magnetite is a mineral, one of the two common naturally occurring iron oxides (chemical formula Fe3O4). Magnetite has been very important in understanding the conditions under which rocks form. Magnetite reacts with oxygen to produce hematite, and the mineral pair forms a buffer that can control oxygen fugacity. *Generally black or silvery, can have a brownish tint.* Iron (III) oxide or ferric oxide is the inorganic compound with the formula Fe2O3. We'd most likely be dealing with alpha-phase ferric oxide because it is the most stable Fe2O3 phase over ~500°C. This one's also called hematite. *Fe2O3 is dark red.* -- The wikipedia page above links to nice summaries of the hydrous oxides as well, if you want to check them out. The variables we have to work with are: the amount of iron in the meteorite, plus abundances of other minerals that could affect oxide or other mineral formation in the crust. Fragment shape and orientation probably control oxygen flow to given areas (see link below) but also -- ...the entry speed/angle and breakup height would probably help to determine the rate of ablation/deceleration of given fragments (e.g. the point at which fusion crust will remain on the surface of the meteorite versus ablating away), which would also affect the temperature at which the remaining fusion crust formed (a potential variable controlling the oxidative state of iron?). Either way, since access to oxygen seems to determine the redness of the fusion crust, altitude of fragmentation is probably quite important. http://www.ebay.com/itm/Chelyabinsk-Meteorite-Fall-from-Feb-15th-2013-in-Russia-7-098-grams-/111073775576?pt=LH_DefaultDomain_0hash=item19dc834fd8 ^One of the better examples currently on ebay, with topographically low areas that clearly show reddening/browning. In short, yes, hematite is red, so hematite content is a good candidate for the 'reddening agent.' But, then...why don't H chondrites usually form such red fusion crusts? It might be due to the higher iron content in H-chondrites and the ratio of iron to oxygen in the above three oxides. Fe2O3 (hematite) has the lowest Fe to O ratio of the above three minerals (1:1 vs. 3:4 vs. 2:3), so a meteorite that is higher in iron might be less likely to form a lower-iron oxide (hematite) in the same conditions. But this seems somewhat unlikely, as this hypothesized cutoff for hematite formation in the crust would depend on the difference in the modal abundance of Fe in L's versus H's, and that's not a clear boundary. One would have to look at the metal content of various larger multiple falls and examine large numbers of pristine stones from each in order to reach a well-supported answer to that question. Chelyabinsk does support this general hypothesis, though. It broke up at a lower altitude than most bolides do, so fragments should have been exposed to a thicker atmosphere/more oxygen in their final ablative stages of flight. Because of this, we'd expect to see more iron oxides with higher ratios of oxygen to iron in the fusion crust (e.g. our red hematite) . Lo and behold, we're seeing more stones with reddish fusion crusts than
Re: [meteorite-list] Red(dish) Fusion Crust
Hi, But, then...why don't H chondrites usually form such red fusion crusts? But they do, the example on Svend's page is a Buzzard Coulee, and in literature you read it about Pultusk. This list seems to have a short memory. Well, the specialty here, is that a colour variation in the crust, if found only on one side, can be used as criterion for orientation. Most of the examples shown here, underline, that stones must have had at least a longer phase of stable flight, because it is indicated by the lipping around the edges of these sides. (Which identify the coloured sides as backsides). Best, Martin __ Visit the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Red(dish) Fusion Crust
Hola, Looking at his pagethe Buzzard is red to a much lesser extent. Good observation, though -- it makes sense that H's would still show at least some hematite presence, if that is was causes the red coloration. The first link in my last email goes against what you say above. Note that the pictured stone has a black, frothy rear and a reddish shield-shaped front. Regards, Jason www.fallsandfinds.com On Wed, May 29, 2013 at 8:41 AM, Martin Altmann altm...@meteorite-martin.de wrote: Hi, But, then...why don't H chondrites usually form such red fusion crusts? But they do, the example on Svend's page is a Buzzard Coulee, and in literature you read it about Pultusk. This list seems to have a short memory. Well, the specialty here, is that a colour variation in the crust, if found only on one side, can be used as criterion for orientation. Most of the examples shown here, underline, that stones must have had at least a longer phase of stable flight, because it is indicated by the lipping around the edges of these sides. (Which identify the coloured sides as backsides). Best, Martin __ Visit the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list __ Visit the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Red(dish) Fusion Crust
Hiho, I'm thrilled, maybe now many readers of the list rush to their drawers and showcases, to look for more examples of other falls, where they thought before, that the lighter colour was due terrestrial oxidation and the individuals not that fresh. Let's wait, what they'll find! Martin -Ursprüngliche Nachricht- Von: Jason Utas [mailto:meteorite...@gmail.com] Gesendet: Mittwoch, 29. Mai 2013 18:02 An: Martin Altmann Betreff: Re: [meteorite-list] Red(dish) Fusion Crust Hola, Looking at his pagethe Buzzard is red to a much lesser extent. Good observation, though -- it makes sense that H's would still show at least some hematite presence, if that is was causes the red coloration. The first link in my last email goes against what you say above. Note that the pictured stone has a black, frothy rear and a reddish shield-shaped front. Regards, Jason www.fallsandfinds.com On Wed, May 29, 2013 at 8:41 AM, Martin Altmann altm...@meteorite-martin.de wrote: Hi, But, then...why don't H chondrites usually form such red fusion crusts? But they do, the example on Svend's page is a Buzzard Coulee, and in literature you read it about Pultusk. This list seems to have a short memory. Well, the specialty here, is that a colour variation in the crust, if found only on one side, can be used as criterion for orientation. Most of the examples shown here, underline, that stones must have had at least a longer phase of stable flight, because it is indicated by the lipping around the edges of these sides. (Which identify the coloured sides as backsides). Best, Martin __ Visit the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list __ Visit the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Red(dish) Fusion Crust
Same as I thought perhaps oxidation on one side of this bensour but now I learn otherwise: http://www.johnsonmeteorites.com/BENSOUR.html Johnson, M.D. www.johnsonmeteorites.com Thumbed on my iPhone On May 29, 2013, at 12:14 PM, Martin Altmann altm...@meteorite-martin.de wrote: Hiho, I'm thrilled, maybe now many readers of the list rush to their drawers and showcases, to look for more examples of other falls, where they thought before, that the lighter colour was due terrestrial oxidation and the individuals not that fresh. Let's wait, what they'll find! Martin -Ursprüngliche Nachricht- Von: Jason Utas [mailto:meteorite...@gmail.com] Gesendet: Mittwoch, 29. Mai 2013 18:02 An: Martin Altmann Betreff: Re: [meteorite-list] Red(dish) Fusion Crust Hola, Looking at his pagethe Buzzard is red to a much lesser extent. Good observation, though -- it makes sense that H's would still show at least some hematite presence, if that is was causes the red coloration. The first link in my last email goes against what you say above. Note that the pictured stone has a black, frothy rear and a reddish shield-shaped front. Regards, Jason www.fallsandfinds.com On Wed, May 29, 2013 at 8:41 AM, Martin Altmann altm...@meteorite-martin.de wrote: Hi, But, then...why don't H chondrites usually form such red fusion crusts? But they do, the example on Svend's page is a Buzzard Coulee, and in literature you read it about Pultusk. This list seems to have a short memory. Well, the specialty here, is that a colour variation in the crust, if found only on one side, can be used as criterion for orientation. Most of the examples shown here, underline, that stones must have had at least a longer phase of stable flight, because it is indicated by the lipping around the edges of these sides. (Which identify the coloured sides as backsides). Best, Martin __ Visit the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list __ Visit the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list __ Visit the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
