[meteorite-list] Tektite identification criterion
From: mafer_at_domafer.com <mafer_at_meteoritecentral.com>
Date: Thu Apr 22 09:53:35 2004 Message-ID: <016001c2a719$a57abaa0$6401a8c0_at_vs.shawcable.net> This is a multi-part message in MIME format. ------=_NextPart_000_015D_01C2A6D6.963282A0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable 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, =20 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. =20 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 =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. =20 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 =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. =20 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. =20 Merry Winter Solstice and a Happy New Orbit to All! =20 Norm (TektiteSource.com) ------=_NextPart_000_015D_01C2A6D6.963282A0 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 content=3D"text/html; charset=3Diso-8859-1" = http-equiv=3DContent-Type> <META content=3D"MSHTML 5.00.2614.3500" name=3DGENERATOR> <STYLE></STYLE> </HEAD> <BODY bgColor=3D#ffffff> <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 or=20 not.</FONT></DIV> <DIV><FONT size=3D2>Mark flexing new old knowledge without a lot of=20 experience</FONT></DIV> <BLOCKQUOTE=20 style=3D"BORDER-LEFT: #000000 2px solid; MARGIN-LEFT: 5px; MARGIN-RIGHT: = 0px; PADDING-LEFT: 5px; PADDING-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 href=3D"mailto:nlehrman_at_nvbell.net" title=3Dnlehrman@nvbell.net>N = Lehrman</A>=20 </DIV> <DIV style=3D"FONT: 10pt arial"><B>To:</B> <A=20 href=3D"mailto:meteorite-list_at_meteoritecentral.com"=20 = title=3Dmeteorite-list_at_meteoritecentral.com>meteorite-list@meteoritecentr= al.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 = find a=20 reasonably simple tektite test that doesn't require an ion beam = microprobe,=20 etc. to do. I've thought about the following approach for a = while,=20 but just never got around to trying it till today. The basic = concept is=20 that true tektites typically contain absolutely no primary = crystallites=20 (except for Muong nongs which occasionally do have remnant mineral = grains from=20 incompletely melted target material). Only crystalline = materials=20 can assume magnetic properties, so without crystals, no magnetic=20 susceptibility. Further, tektite glass is highly reduced (i.e., = low=20 volatile Oxygen), so even if it were to have microcrystals, they would = not be=20 magnetite. The black or green color of tektite glass is from = elemental=20 iron literally dissolved in the glass, in which form it has no = magnetic=20 properties.<BR><BR>On the other hand, nearly all volcanic glasses = contain=20 crystallites or phenocrysts. Since iron is abundant in the = earth's crust=20 and magnetite crystallizes at relatively high temperatures, it = is an=20 early-forming mineral---that is, if there were any crystals starting = to form,=20 magnetite would likely be there. Magnetite is, in = fact,=20 common in obsidian, sometimes 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 meter=20 available to me through work (mag susc. basically relates to the = volume=20 content of magnetic minerals like magnetite, titanomagnetite, = ilmenite,=20 pyrrhotite and native iron). In effect, the magnetic properties = of the=20 specimen provide an indirect way of assessing the presence of = crystallites AND=20 the redox state of the material, both of which are good solid criteria = for=20 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=20 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 = 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 is=20 that when faced with a suspect tektite, test for subtle magnetic=20 properties. They may not always be detected by the simple magnet = 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 of=20 you, but what you've just read is to my knowledge the first suggested = simple=20 field test to discriminate between tektites, terrestrial volcanics, = and=20 impactites. Of course, there are exceptions to most every rule, = but so=20 far it's looking to me like this will put you on the right side of 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 to=20 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></FONT></BODY></HTML> ------=_NextPart_000_015D_01C2A6D6.963282A0-- Received on Wed 18 Dec 2002 11:46:49 PM PST |
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