[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>

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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)

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<META http-equiv=3DContent-Type content=3D"text/html; =
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<BODY bgColor=3D#ffffff>
<DIV><FONT size=3D2>Mark and list,</FONT></DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</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>&nbsp;</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?".&nbsp; =
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>&nbsp;</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.&nbsp; The really big challenge though is coming up with =
criteria that=20
can be used outside of a major university laboratory setting.&nbsp; For =
example,=20
one of the hallmark characteristics of tektite glass is its exceedingly =
low=20
water content.&nbsp; 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.&nbsp; Ditto a good ion microprobe=20
analysis.&nbsp; 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>&nbsp;</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.&nbsp; You =

meteorite freaks know the routine well---and have developed a pretty =
good bag of=20
tricks to screen the winners from the losers.&nbsp; With tektites, we've =
barely=20
emerged from debating the very definition of the word.&nbsp; =
</FONT></DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2>Cheers,</FONT></DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</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>&nbsp;</DIV>
  <DIV><FONT size=3D2>Norm, are there any other tests that may prove =
useful like=20
  refractive indice, specific gravity or thermal conductivity?&nbsp; 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>&nbsp;</DIV>
    <DIV align=3Djustify><FONT size=3D2><STRONG>New =
subject!</STRONG>&nbsp; At the=20
    TektiteSource.com, we've been bombarded with a stream of tektite =
wannabes=20
    (Texas, Arizona, Tanzania----).&nbsp; I've been struggling&nbsp;to=20
    find&nbsp;a reasonably simple tektite test that doesn't require an =
ion beam=20
    microprobe, etc. to do.&nbsp; I've thought about the =
following&nbsp;approach=20
    for a while, but just never got around to trying it till =
today.&nbsp; 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).&nbsp; =
Only&nbsp;=20
    crystalline materials can assume magnetic properties, so without =
crystals,=20
    no magnetic susceptibility.&nbsp; 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.&nbsp; 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.&nbsp; Since iron is =
abundant in=20
    the earth's crust and magnetite&nbsp; crystallizes at relatively =
high=20
    temperatures, it is an early-forming mineral---that is, if there =
were any=20
    crystals starting to form, &nbsp;magnetite would likely be=20
    there.&nbsp;&nbsp;Magnetite is, in fact, common in obsidian, =
sometimes=20
    causing the black coloration.</FONT></DIV>
    <DIV align=3Djustify><FONT size=3D2></FONT>&nbsp;</DIV>
    <DIV align=3Djustify><FONT size=3D2>From this line of thought, a =
fairly simple=20
    test is obvious: check for magnetic properties.&nbsp; To =
nail&nbsp;this down=20
    in more&nbsp;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).&nbsp; 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.&nbsp; =
</FONT></DIV>
    <DIV align=3Djustify><FONT size=3D2></FONT>&nbsp;</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:&nbsp; 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.&nbsp; 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>&nbsp;</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.&nbsp; I tried&nbsp;a suspended=20
    neodymium/samarium&nbsp;magnet and got no reaction on any of my =
actual=20
    tektites.&nbsp; 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.&nbsp;</FONT></DIV>
    <DIV align=3Djustify><FONT size=3D2></FONT>&nbsp;</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.&nbsp; 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>&nbsp;</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.&nbsp; 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>&nbsp;</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>&nbsp;</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>

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Received on Thu 19 Dec 2002 02:24:49 AM PST


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