[meteorite-list] Tektite identification criterion
From: N Lehrman <nlehrman_at_meteoritecentral.com>
Date: Thu Apr 22 09:53:35 2004 Message-ID: <026501c2a72f$b78f0460$19e3fea9_at_homeportal.2wire.net> This is a multi-part message in MIME format. ------=_NextPart_000_0262_01C2A6EC.A9070F20 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Mark and list, Properties like those you've listed do show helpful variations, but the = range between individual tektite types tends to overlap with terrestrial = materials to the point that none of this allows one to discriminate = between tektites and other materials. Despite the thousands of papers debating the myriad mysteries of tektite = lore, I don't know of any that directly address the fundamental question = "how do you tell if something is or is not a tektite?". I'd love to = hear from any of you out there with ideas or suggested references. I'm going to pull a synthesis of this subject together with time, and = there is a reasonable stash of widely scattered data that bear on the = subject. The really big challenge though is coming up with criteria = that can be used outside of a major university laboratory setting. For = example, one of the hallmark characteristics of tektite glass is its = exceedingly low water content. However, you'd be hard pressed to find = any commercial laboratory that could provide an accurate determination = of this property at the levels of resolution we require. Ditto a good = ion microprobe analysis. This is all great stuff in the academic = laboratory settings where most technical publications originate, but = what are we supposed to do out here on the front lines? Of course, there are great folks in academia who will collaborate on = worthy issues, but such matters cannot extend to passing judgment on = suspect materials that arrive in the mail every other week. You = meteorite freaks know the routine well---and have developed a pretty = good bag of tricks to screen the winners from the losers. With = tektites, we've barely emerged from debating the very definition of the = word. =20 Cheers, Norm (TektiteSource.com) ----- Original Message -----=20 From: mafer_at_domafer.com=20 To: N Lehrman=20 Cc: meteorite-list_at_meteoritecentral.com=20 Sent: Wednesday, December 18, 2002 8:46 PM Subject: Re: [meteorite-list] Tektite identification criterion Hi Norm and list Norm, are there any other tests that may prove useful like refractive = indice, specific gravity or thermal conductivity? I mention these = because of tektites having mineral contents not normally associated with = terrestrial rock or glass, and I don't know if tachylytes would be of = concern or not. Mark flexing new old knowledge without a lot of experience ----- Original Message -----=20 From: N Lehrman=20 To: meteorite-list_at_meteoritecentral.com=20 Sent: Wednesday, December 18, 2002 8:46 PM Subject: [meteorite-list] Tektite identification criterion List, New subject! At the TektiteSource.com, we've been bombarded with a = stream of tektite wannabes (Texas, Arizona, Tanzania----). I've been = struggling to find a reasonably simple tektite test that doesn't require = an ion beam microprobe, etc. to do. I've thought about the following = approach for a while, but just never got around to trying it till today. = The basic concept is that true tektites typically contain absolutely no = primary crystallites (except for Muong nongs which occasionally do have = remnant mineral grains from incompletely melted target material). Only = crystalline materials can assume magnetic properties, so without = crystals, no magnetic susceptibility. Further, tektite glass is highly = reduced (i.e., low volatile Oxygen), so even if it were to have = microcrystals, they would not be magnetite. The black or green color of = tektite glass is from elemental iron literally dissolved in the glass, = in which form it has no magnetic properties. On the other hand, nearly all volcanic glasses contain crystallites = or phenocrysts. Since iron is abundant in the earth's crust and = magnetite crystallizes at relatively high temperatures, it is an = early-forming mineral---that is, if there were any crystals starting to = form, magnetite would likely be there. Magnetite is, in fact, common = in obsidian, sometimes causing the black coloration. From this line of thought, a fairly simple test is obvious: check = for magnetic properties. To nail this down in more quantified terms, I = used a digital magnetic susceptibility meter available to me through = work (mag susc. basically relates to the volume content of magnetic = minerals like magnetite, titanomagnetite, ilmenite, pyrrhotite and = native iron). In effect, the magnetic properties of the specimen = provide an indirect way of assessing the presence of crystallites AND = the redox state of the material, both of which are good solid criteria = for tektites vs. terrestrial volcanics. =20 I'll post details after they're a bit more refined, but the basic = pattern matches the theory: true tektites have extremely low magnetic = susceptibilities; obsidians, apache tears, and amerikanites all yield = values 2 to 10 times higher, with no field of overlap. Impactites = (which very commonly contain Ni-Fe inclusions, are commonly 1 to 2 = orders of magnitude higher than the tektites. Most people don't have access to a magnetic susceptibility meter, = but these differences are sufficiently large to detect with a strong = magnet. I tried a suspended neodymium/samarium magnet and got no = reaction on any of my actual tektites. I did get subtle deflections = with the tektite wannabes I was checking, and it goes without saying = that some of the impactites jumped out and clung to the magnet.=20 The sweet and simple conclusion to all this is that when faced with = a suspect tektite, test for subtle magnetic properties. They may not = always be detected by the simple magnet test---but if the material = deflects a strong magnet, it's not a tektite. This may seem like esoteric trivia to some of you, but what you've = just read is to my knowledge the first suggested simple field test to = discriminate between tektites, terrestrial volcanics, and impactites. = Of course, there are exceptions to most every rule, but so far it's = looking to me like this will put you on the right side of the argument = about 99% of the time. Merry Winter Solstice and a Happy New Orbit to All! Norm (TektiteSource.com) ------=_NextPart_000_0262_01C2A6EC.A9070F20 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META http-equiv=3DContent-Type content=3D"text/html; = charset=3Diso-8859-1"> <META content=3D"MSHTML 6.00.2600.0" name=3DGENERATOR> <STYLE></STYLE> </HEAD> <BODY bgColor=3D#ffffff> <DIV><FONT size=3D2>Mark and list,</FONT></DIV> <DIV><FONT size=3D2></FONT> </DIV> <DIV><FONT size=3D2>Properties like those you've listed do show helpful=20 variations, but the range between individual tektite types tends to = overlap with=20 terrestrial materials to the point that none of this allows one to = discriminate=20 between tektites and other materials.</FONT></DIV> <DIV><FONT size=3D2></FONT> </DIV> <DIV><FONT size=3D2>Despite the thousands of papers debating the myriad = mysteries=20 of tektite lore, I don't know of any that directly address the = fundamental=20 question "how do you tell if something is or is not a tektite?". = I'd love=20 to hear from any of you out there with ideas or suggested=20 references.</FONT></DIV> <DIV><FONT size=3D2></FONT> </DIV> <DIV><FONT size=3D2>I'm going to pull a synthesis of this subject = together with=20 time, and there is a reasonable stash of widely scattered data that bear = on the=20 subject. The really big challenge though is coming up with = criteria that=20 can be used outside of a major university laboratory setting. For = example,=20 one of the hallmark characteristics of tektite glass is its exceedingly = low=20 water content. However, you'd be hard pressed to find any = commercial=20 laboratory that could provide an accurate determination of this property = at the=20 levels of resolution we require. Ditto a good ion microprobe=20 analysis. This is all great stuff in the academic laboratory = settings=20 where most technical publications originate, but what are we supposed to = do out=20 here on the front lines?</FONT></DIV> <DIV><FONT size=3D2></FONT> </DIV> <DIV><FONT size=3D2>Of course, there are great folks in academia who = will=20 collaborate on worthy issues, but such matters cannot extend to passing = judgment=20 on suspect materials that arrive in the mail every other week. You = meteorite freaks know the routine well---and have developed a pretty = good bag of=20 tricks to screen the winners from the losers. With tektites, we've = barely=20 emerged from debating the very definition of the word. = </FONT></DIV> <DIV><FONT size=3D2></FONT> </DIV> <DIV><FONT size=3D2>Cheers,</FONT></DIV> <DIV><FONT size=3D2></FONT> </DIV> <DIV><FONT size=3D2>Norm</FONT></DIV> <DIV><FONT size=3D2>(TektiteSource.com)</FONT></DIV> <BLOCKQUOTE dir=3Dltr=20 style=3D"PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; = BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px"> <DIV style=3D"FONT: 10pt arial">----- Original Message ----- </DIV> <DIV=20 style=3D"BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: = black"><B>From:</B>=20 <A title=3Dmafer_at_domafer.com=20 href=3D"mailto:mafer_at_domafer.com">mafer@domafer.com</A> </DIV> <DIV style=3D"FONT: 10pt arial"><B>To:</B> <A = title=3Dnlehrman_at_nvbell.net=20 href=3D"mailto:nlehrman_at_nvbell.net">N Lehrman</A> </DIV> <DIV style=3D"FONT: 10pt arial"><B>Cc:</B> <A=20 title=3Dmeteorite-list_at_meteoritecentral.com=20 = href=3D"mailto:meteorite-list_at_meteoritecentral.com">meteorite-list@meteor= itecentral.com</A>=20 </DIV> <DIV style=3D"FONT: 10pt arial"><B>Sent:</B> Wednesday, December 18, = 2002 8:46=20 PM</DIV> <DIV style=3D"FONT: 10pt arial"><B>Subject:</B> Re: [meteorite-list] = Tektite=20 identification criterion</DIV> <DIV><BR></DIV> <DIV><FONT size=3D2>Hi Norm and list</FONT></DIV> <DIV> </DIV> <DIV><FONT size=3D2>Norm, are there any other tests that may prove = useful like=20 refractive indice, specific gravity or thermal conductivity? I = mention=20 these because of tektites having mineral contents not normally = associated with=20 terrestrial rock or glass, and I don't know if tachylytes would be of = concern=20 or not.</FONT></DIV> <DIV><FONT size=3D2>Mark flexing new old knowledge without a lot of=20 experience</FONT></DIV> <BLOCKQUOTE=20 style=3D"PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; = BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px"> <DIV style=3D"FONT: 10pt arial">----- Original Message ----- </DIV> <DIV=20 style=3D"BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: = black"><B>From:</B>=20 <A title=3Dnlehrman_at_nvbell.net href=3D"mailto:nlehrman@nvbell.net">N = Lehrman</A>=20 </DIV> <DIV style=3D"FONT: 10pt arial"><B>To:</B> <A=20 title=3Dmeteorite-list_at_meteoritecentral.com=20 = href=3D"mailto:meteorite-list_at_meteoritecentral.com">meteorite-list@meteor= itecentral.com</A>=20 </DIV> <DIV style=3D"FONT: 10pt arial"><B>Sent:</B> Wednesday, December 18, = 2002 8:46=20 PM</DIV> <DIV style=3D"FONT: 10pt arial"><B>Subject:</B> [meteorite-list] = Tektite=20 identification criterion</DIV> <DIV><BR></DIV> <DIV><FONT size=3D2>List,</FONT></DIV> <DIV align=3Djustify><FONT size=3D2></FONT> </DIV> <DIV align=3Djustify><FONT size=3D2><STRONG>New = subject!</STRONG> At the=20 TektiteSource.com, we've been bombarded with a stream of tektite = wannabes=20 (Texas, Arizona, Tanzania----). I've been struggling to=20 find a reasonably simple tektite test that doesn't require an = ion beam=20 microprobe, etc. to do. I've thought about the = following approach=20 for a while, but just never got around to trying it till = today. The=20 basic concept is that true tektites typically contain absolutely no = primary=20 crystallites (except for Muong nongs which occasionally do have = remnant=20 mineral grains from incompletely melted target material). = Only =20 crystalline materials can assume magnetic properties, so without = crystals,=20 no magnetic susceptibility. Further, tektite glass is highly = reduced=20 (i.e., low volatile Oxygen), so even if it were to have = microcrystals, they=20 would not be magnetite. The black or green color of tektite = glass is=20 from elemental iron literally dissolved in the glass, in which form = it has=20 no magnetic properties.<BR><BR>On the other hand, nearly all = volcanic=20 glasses contain crystallites or phenocrysts. Since iron is = abundant in=20 the earth's crust and magnetite crystallizes at relatively = high=20 temperatures, it is an early-forming mineral---that is, if there = were any=20 crystals starting to form, magnetite would likely be=20 there. Magnetite is, in fact, common in obsidian, = sometimes=20 causing the black coloration.</FONT></DIV> <DIV align=3Djustify><FONT size=3D2></FONT> </DIV> <DIV align=3Djustify><FONT size=3D2>From this line of thought, a = fairly simple=20 test is obvious: check for magnetic properties. To = nail this down=20 in more quantified terms, I used a digital magnetic = susceptibility=20 meter available to me through work (mag susc. basically relates to = the=20 volume content of magnetic minerals like magnetite, titanomagnetite, = ilmenite, pyrrhotite and native iron). In effect, the magnetic = properties of the specimen provide an indirect way of assessing the = presence=20 of crystallites AND the redox state of the material, both of which = are good=20 solid criteria for tektites vs. terrestrial volcanics. = </FONT></DIV> <DIV align=3Djustify><FONT size=3D2></FONT> </DIV> <DIV align=3Djustify><FONT size=3D2>I'll post details after they're = a bit more=20 refined, but the basic pattern matches the theory: true = tektites have=20 extremely low magnetic susceptibilities; obsidians, apache tears, = and=20 amerikanites all yield values 2 to 10 times higher, with no field of = overlap. Impactites (which very commonly contain Ni-Fe = inclusions, are=20 commonly 1 to 2 orders of magnitude higher than the = tektites.</FONT></DIV> <DIV align=3Djustify><FONT size=3D2></FONT> </DIV> <DIV align=3Djustify><FONT size=3D2>Most people don't have access to = a magnetic=20 susceptibility meter, but these differences are sufficiently large = to detect=20 with a strong magnet. I tried a suspended=20 neodymium/samarium magnet and got no reaction on any of my = actual=20 tektites. I did get subtle deflections with the tektite = wannabes I was=20 checking, and it goes without saying that some of the impactites = jumped out=20 and clung to the magnet. </FONT></DIV> <DIV align=3Djustify><FONT size=3D2></FONT> </DIV> <DIV align=3Djustify><FONT size=3D2>The sweet and simple conclusion = to all this=20 is that when faced with a suspect tektite, test for subtle magnetic=20 properties. They may not always be detected by the simple = magnet=20 test---but if the material deflects a strong magnet, it's not a=20 tektite.</FONT></DIV> <DIV align=3Djustify><FONT size=3D2></FONT> </DIV> <DIV align=3Djustify><FONT size=3D2>This may seem like esoteric = trivia to some=20 of you, but what you've just read is to my knowledge the first = suggested=20 simple field test to discriminate between tektites, terrestrial = volcanics,=20 and impactites. Of course, there are exceptions to most every = rule,=20 but so far it's looking to me like this will put you on the right = side of=20 the argument about 99% of the time.</FONT></DIV> <DIV align=3Djustify><FONT size=3D2></FONT> </DIV> <DIV align=3Djustify><FONT size=3D2>Merry Winter Solstice and a = Happy New Orbit=20 to All!</FONT></DIV> <DIV align=3Djustify><FONT size=3D2></FONT> </DIV> <DIV align=3Djustify><FONT size=3D2>Norm</FONT></DIV> <DIV align=3Djustify><FONT=20 size=3D2>(TektiteSource.com)</DIV></BLOCKQUOTE></BLOCKQUOTE></FONT></BODY= ></HTML> ------=_NextPart_000_0262_01C2A6EC.A9070F20-- Received on Thu 19 Dec 2002 02:24:49 AM PST |
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