[meteorite-list] THEORIES OF THE ORIGIN OF TEKTITES, Part Two
From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Tue Feb 28 14:16:10 2006
Hi, Norm, List,
My apologies. This statement of mine was
a complete and total error. I have no idea where
I got this idea, because it is obviously untrue, and
on some level I knew that.
I offer a fistful of excuses: it was written very late
at night; I was coming down with something nasty
in the head cold department; a cosmic ray flipped
a bit in some brain cell...
Tell the waiter I like my crow well done...
Sterling K. Webb
----- Original Message -----
From: "Norm Lehrman" <nlehrman_at_nvbell.net>
To: "Sterling K. Webb" <sterling_k_webb_at_sbcglobal.net>; "Meteorite List"
Sent: Monday, February 20, 2006 10:05 PM
Subject: Re: [meteorite-list] THEORIES OF THE ORIGIN OF TEKTITES, Part Two
> Thanks for posting this series! One question though:
> Item #5: "It would also appear that no one tried
> breaking a specimen of each, as the fracture
> morphology of each differs."
> In what way? I've never tried breaking specimens, but
> I've seen plently of broken ones and have never
> noticed a difference. As amorphous glass, both
> obsidian and tektites have a nice conchoidal fracture.
> However, now that you bring it to my attention, I can
> imagine a theoretical difference: since most obsidian
> does have tiny crystallites, and tektites have
> absolutely none, tektites should have a smoother
> fracture surface, relatively free of stair-steps.
> I'll have to go check as soon as I get this written.
> As an interesting aside, various obsidians were
> esteemed for varied uses in the stone age. Varieties
> packed with incipient crystals flaked more crudely
> than more pure glasses, but because the tiny crystals
> obstructed the growth of fractures, tools made of such
> impure material were tougher. Better coarse, heavy
> duty implements could be made of this. More pure
> glasses made for perfectly flaked extra sharp
> arrowheads, but they were essentially one-use items as
> they broke very easily (there being no crystallites to
> interfere with fracture growth).
> Is this the sort of difference in fracture morphology
> to which you refer?
> --- "Sterling K. Webb" <sterling_k_webb_at_sbcglobal.net>
>> Part Two of
>> THEORIES OF THE ORIGIN OF TEKTITES
>> Passing through the Colossally Silly Entrance Hall,
>> we next enter the
>> extensive and colorful Volcanic Tektite Exhibition.
>> 5. The Terrestrial Volcanic Origin of Tektites:
>> Mayer, in 1788, published
>> the first scientific tektite theory; he called
>> moldavites "glassy lavas."
>> Charles Darwin, in 1844 (The Voyage of the H.M.S.
>> Beagle), first described
>> australite "buttons" and identified them as
>> obsidian. He wondered a great
>> deal about their unique shape, but became distracted
>> by some issue or other
>> in biology, so the world lost a great tektite
>> The volcanic theory became as predominant in the
>> 19th Century as the Impact
>> Theory is today. It was endorsed by Wickman, 1893;
>> van Dijk, 1879; W. D.
>> Campbell, 1906; La Conte, 1902; and Moore, 1916 (who
>> said tektites were
>> identical to "Pele's Tears"); Simpson , 1902,
>> proposed Australite tektites
>> came from Krakatoa. Dunn, 1908 and 1912, proposed a
>> complicated formation of
>> tektites inside of gas bubbles in fresh lava, a
>> suggestion further developed
>> and complicated by Buddhue in 1940, while Dunn then
>> later (1935) suggested
>> tektites were formed by rain and snow falling on
>> molten lava.
>> The volcanic theories all died when geochemical
>> analysis advances in the
>> 20th Century, as tektites have a composition that is
>> quite different from
>> any terrestrial volcanic rock, and tektites are
>> easily distinguishable from
>> obsidian. It should be pointed out, in defense of
>> Darwin and all the early
>> geologists, that just from the standpoint of holding
>> a tektite and obsidian
>> in your hand and looking at them, they appear to be
>> materially identical.
>> Chemical and physical analysis is required to
>> distinguish them. It would
>> also appear that no one tried breaking a specimen of
>> each, as the fracture
>> morphology of each differs.
>> However, the last Terrestrial Volcanic Theory was
>> proposed in 1976! It is:
>> 6. The "Cryptovolcanic" Origin of Tektites: McCall,
>> 1976: To understand this
>> at all, we need to dig into the strange tribal
>> relationships of science.
>> British geologists ("we invented geology, you know")
>> were firmly wedded
>> (possibly even welded) to the volcanic origin of
>> craters, all craters, of
>> all kinds, on all worlds. An immense amount of
>> energy and thought had been
>> invested in lunar volcanic theory in particular, up
>> through the 1950's.
>> Those who learned their geology at British
>> institutions (Australians, New
>> Zedders, and so forth) were trained in this
>> tradition. The notion of that
>> some craters on the Earth or elsewhere might have
>> been formed by heavy
>> objects falling out of the sky was regarded as a
>> crackpot theory put forward
>> entirely by brash and uninformed colonials of the
>> American variety who were
>> well-known to be fond of whizz-bangs ("child-like,
>> you know"), and the
>> impact theory was resolutely resisted as errant
>> nonsense up until the moment
>> of the Moon landings, when it all unraveled in a
>> A "volcanic" explanation was handy; there had always
>> been craters from which
>> volcanic characteristics were absent. They were
>> called by these geologists
>> "cryptovolcanic," meaning that their volcanic
>> origins were hidden. This was
>> a theory built on the absence of evidence as a proof
>> of the theory, always a
>> dangerous logical method. Cryptovolcanic craters
>> were postulated to be the
>> result of direct venting of very deep, very hot,
>> high pressure gassy magma
>> to the surface of the planet in a manner analogous
>> to kimberlite pipes.
>> Advances of all kinds, but specifically in the
>> ability to visualize deep
>> strata make "cryptovulcanism" a bad historical joke.
>> McCall, an Australian geologist and a good one, too,
>> put forward a theory of
>> the cryptovolcanic origin of tektites in 1976. He
>> also disbelieved in the
>> impact origin of terrestrial craters and of
>> extra-terrestrial craters, lunar
>> craters, etc. This, in the post-Apollo era!
>> McCall was neither stupid nor uninformed and he
>> fought a sharp rear-guard
>> action, to his credit. He was honest enough to point
>> out that his own theory
>> was ruined by its inability to explain how you get
>> tektites out of the
>> Earth's atmosphere (to then fall back) without
>> ablating them up completely!
>> Leaving the Volcanic Tektite Exhibition Hall, we
>> enter the spacious
>> Semi-Extra-Terrestrial Pavilion.
>> Continued in Part Three...
>> Sterling K. Webb
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Received on Tue 28 Feb 2006 02:16:01 PM PST