[meteorite-list] triolite inclusions
From: John Keefner <jk_unlimited_at_meteoritecentral.com>
Date: Mon Jan 3 12:54:06 2005 Message-ID: <BAY101-F288ED687F751DFEA885961FE900_at_phx.gbl> Hi all, A quick question regarding rounded troilite inclusions in iron meteorites... I believe FeS has a significantly lower melting temperature (around 1000 degrees C) than the Fe-Ni alloy (around 1450 degrees C) that make most iron meteorites. In a cooling planetismal, wouldn't one expect that troilite would be the last dregs of molten liquid remaining in the cracks between crystallized Fe-Ni? If that were the case, wouldn't troilite be expected to be a 'filler', with an elongated morphology? So, why does troilite occur in rounded inclusions? Perhaps rounding from grain boundary diffusion occurs on a long time-scale or the blebs are an indication of late stage impact melting and rapid cooling... I'm not sure that I buy the surface tension idea where troilite separates out from an ocean of liquid Fe-Ni alloy. Thanks, John From: MexicoDoug_at_aol.com To: steve_arnol60120_at_yahoo.com, meteorite-list@meteoritecentral.com Subject: Re: [meteorite-list] triolite inclusions Date: Mon, 3 Jan 2005 11:51:26 EST Hola Steve, I think Tri-o-lite is a dead brand of the dead Urelite Corporation. On the other hand, Troilite, named for the Italian Jesuita Abbé Domenico Troili of Villa Albareto meteorite fame. The 1766 Italian witnessed fall, Troili collected eyewitness accounts of what he actually believed was a volcanic discharge into the atmosphere. Troilite was named after him since he collected some of the stones - yes it was first observed in "modern" times from the University of Modena, Ferrari town, Italy, in this L5 stone meteorite. EvNot an iron meteorite. Troilite's account led it to be understood as pyrite (fool's gold), but a few decades later Howard of Howardite fame set the woirld straight on thatshowing it was an iron sulfide but different from the earthly ones because it was NON-magnetic, unlike the earthly counterparts. Anyway in 1863 Troili got the honor and it was named "Troilit" by Rose in Berlin after he demonstrated that it was balanced FeS and recognized Troili's attempt at description of it nearly one hundred years earlier. In English, Troilit would be Troilite... So...Troilite is just a charged balanced Fe-S hexoganol pyrrhotite, in other words, ferrous sulfide. Why it gets into the iron meteorites to me is a question with philosophical overtones like why is the sky blue. The stuff is found in many mines as pyrrhotite, the similar earthly mineral which almost always has an excess of sulfur with it. In other words, FeS iron defficient where both have a plus two valence shell. But if you look at it another way, considering the interior of planetesimals iron meteorite foundries, you might say the creator accidentally contaminated the iron with sulphur. That is why if you grind the mineral your pet blobs can stink on ice like rotten eggs. Sulfur isn't the only contaminant in the meteoritical material. There is a host of stuff like Iriduim in traces, too. Or oxygen in carbonaceous meteorites. So where you get a nice oxide with oxygen, you might get a nice sulfide with sulfur. Putting the sulfur in the foundry and then getting the blobules you like might be caused by physical events internal in the meteoritical foundary. Perhaps when all is molten to start with, the iron nickel form a nice alloy not too miscible with the troilite, so they naturally separate, just like you shaking up a bottle with oil and water and watching the blobs form of the separate phases (aquaeous and organic). Or perhaps the high pressuressquish it into imperfections in the iron nickel alloy as it cools, like squashing a Miller can in your hands, maybe it sort of aggregates through the conduits that are available. But that really isn't likely in my opinion as the first, because they are usually rounded or spheroidal indicating more of a miscibility (mix-separation) issue. A sphere like shape is formed because it minimizes the surface exposed for a given volume when stuck in an unfriendly environment. That's why babies are in the fetal position and girlfriends too, when they are left cold and alone.:) And raindrops look that way and maybe tektites sort of, too... Troilite by no means is limited to occur in iron meteorites, so the creator has contaminated stoney meteorites with it too, as was first observed meticulously by Troili.and there is some in the samples of lunar soil brought back from the Apollo missions as well. Hope this helps your thirst for knowledgof the rockin our showcases.... Saludos and thanks for the Christmas present "freebee", Doug ______________________________________________ Meteorite-list mailing list Meteorite-list_at_meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list Received on Mon 03 Jan 2005 12:53:03 PM PST |
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