[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 Message-ID: <003b01c63c9b$69c73c20$82704b44_at_ATARIENGINE> 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" <meteorite-list_at_meteoritecentral.com> Sent: Monday, February 20, 2006 10:05 PM Subject: Re: [meteorite-list] THEORIES OF THE ORIGIN OF TEKTITES, Part Two > Sterling, > > 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? > > Thanks, > Norm > http://tektitesource.com > > --- "Sterling K. Webb" <sterling_k_webb_at_sbcglobal.net> > wrote: > >> Hi, >> >> 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 >> theorist. >> 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 >> snap. >> >> 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 >> >> >> >> >> ______________________________________________ >> Meteorite-list mailing list >> Meteorite-list_at_meteoritecentral.com >> > http://six.pairlist.net/mailman/listinfo/meteorite-list >> > > ______________________________________________ > Meteorite-list mailing list > Meteorite-list_at_meteoritecentral.com > http://six.pairlist.net/mailman/listinfo/meteorite-list > Received on Tue 28 Feb 2006 02:16:01 PM PST |
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