[meteorite-list] Tektite Presentation

From: Michael Gilmer <meteoritemike_at_meteoritecentral.com>
Date: Mon, 21 Feb 2011 21:37:48 -0500
Message-ID: <AANLkTi=RmdkQhk_JMQKg0YSj=XWoOtAqnb+YZDYxRi6K_at_mail.gmail.com>

Aubrey,

Reading what you say about tektites makes them sound infinitely more
interesting each time you post. I recently spent about an hour on
your website, just reading, learning and enjoying the photos. Great
job and keep up the good work. :)

Best regards,

MikeG


On 2/21/11, Aubrey Whymark <tinbider at yahoo.co.uk> wrote:
> Hi Norm and list
>
> I started out thinking that Splashforms formed by contact with the ground,
> but this is not possible because of the bald spots. The bald spots, as you
> know, formed by spalling - so why just the anterior margin if the tektite
> splatted on the ground - bald spots should be all over. Secondly the shape
> of some of the tektites does not make sense. Take the Hershey's Kiss
> example. These should not exist as in longer teardrops the stable
> orientation is not vertical. In fact the only way these morphologies could
> form is if they formed within the atmosphere whilst the tektite still had
> inherited cosmic velocity and was still probably travelling up. Another
> point - large discs - the anterior depression, which I call a sump, is
> usually not central. This is consistent with atmospheric production. There
> is no doubt in my mind, whatsoever, that Indochinites formed within the
> atmosphere - some during the upward phase, some in the downwards journey.
> Indochinites never
> truely left the atmosphere.
>
> The 'vertibrae' tektites are real rare and might just be freaks (like really
> rarely we come across Philippinites that appear to have two anteriors. The
> blunt area on an asymmetrical dumbbell is caused by late stage spalling
> (same as a bald spot). I guess the 'vertibrea' may form in the same way -
> maybe one end spalls, this changes the balance of the specimen leading to
> the other end spalling.
>
> Interesting what you say about Australites and certainly worth more thought.
> I don't believe any wind tunnel experiment has, however, truely replicated
> tektite formation in terms of true velocity of 8-11 km/sec. Might be wrong -
> will read up again. You do need the ablation first though to explain why
> distal Australite cores are bulbous, whereas more proximal australites are
> often less bulbous and then Philippinites are typically shield-like. Clearly
> the ablation stage protects the tektite somewhat in carrying the heat away.
> Personally I am always interested why almost all Australites are oriented
> whereas Philippinites are most commonly oriented, but unoriented specimens
> are not uncommon. I guess it's simply due to distance travelled, with a much
> greater time for Australites to find a stable orientation.
>
> Back to Philippinites - most are spherical. Teardrops are very very very
> rare. When you find them though, they are very interesting. A few show
> subtle distortion suggestive of atmospheric deformation, presumably on the
> way up. I even have two 'stretch' Philippinites. Sure they are on the
> website somewhere - http://www.tektites.co.uk/stretch.html. These are not
> like the classic Indochinite stretchforms, but clearly show stretching where
> two parts of the tektite are more solid than another as evidenced by
> stretched vs round bubbles. This deformation, again must have occurred on
> the way-up. Come to the biggest Philippinites 10cm diameter +. These
> normally show some degree of spalling and are off-spherical, but take the
> primary surface and they were spherical bodies. Even the largest
> Philippinites entered with a solid exterior, exactly as one would expect
> from cooling experiments. So the vast majority of Philippinites probably
> formed in 'space' as oppose to
> within the 'atmosphere', but a few may have been distorted in the upper
> reaches of the atmosphere as they exited.
>
> Regards, Aubrey
>
>
> --- On Mon, 21/2/11, Norm Lehrman <nlehrman at nvbell.net> wrote:
>
>> From: Norm Lehrman <nlehrman at nvbell.net>
>> Subject: Re: [meteorite-list] Tektite Presentation
>> To: "Aubrey Whymark" <tinbider at yahoo.co.uk>
>> Date: Monday, 21 February, 2011, 14:52
>> Aubrey,
>>
>> Good stuff! There are are a few things I will need to
>> think about. You've
>> offered some truly fresh ideas.
>>
>> For example, I've always assumed that the "splatting" of
>> advanced splashforms
>> was the result of impact with the ground, whereas you do it
>> with air resistance.
>> Could be right, but I'll need to sleep on it a bit. One
>> observation that has me
>> stumped may bear on the question: Hershey's Kisses and
>> their
>> shorter-remnant-tailed splatforms almost always show
>> flow-banding that reflects
>> a differential twist between the tail and the main body.
>> This means that
>> something retarded the spin of one part or the other. I
>> have been thinking that
>> a spinning body splatting onto the ground would be abruptly
>> anchored while the
>> tail carries on for another half-twist or so. Would
>> friction with a compressed
>> air cushion achieve the same? Maybe... Also, I have
>> always struggled with the
>> fact that the splatted basal surface never molds itself
>> around a pebble or piece
>> of vegetative matter. Not once in hundreds of thousands
>> of specimens I have
>> handled. I have a few that look like they formed over
>> another tektite---but if
>> so, we should occasionally find a couple welded together.
>> Your version of
>> splatting against compressed air solves that problem. On
>> the other hand, I have
>> lots of what I call "vertibrae", dumbells with flattened
>> ends. I presume these
>> form by cartwheeling across the ground. This strikes me
>> as harder to do against
>> air.
>>
>> On australites, I have strong reservations that
>> flow-ablating routinely preceeds
>> spalling. For sure, flow-ablated lipped pie-wedges do
>> spall off. I have many
>> examples. But in wind-tunnel experiments, no one has been
>> able to get a sphere
>> to flow-ablate into a flanged disk. All of the successful
>> runs started with
>> pre-formed lenses, which would suggest in nature the
>> primary sphere may first
>> spall to form a core, then progress into a flanged button
>> (which may itself go
>> through a phase of second-generation spalling).
>>
>> I've gotta run. More later. (In Johannesburg heading
>> for Ghana---)
>>
>> Norm
>>
>>
>>
>> ----- Original Message ----
>> From: Aubrey Whymark <tinbider at yahoo.co.uk>
>> To: meteorite list <meteorite-list at meteoritecentral.com>
>> Sent: Mon, February 21, 2011 3:26:05 PM
>> Subject: [meteorite-list] Tektite Presentation
>>
>> Hi
>>
>> For those interested in tektites, then you might be
>> interested to view the
>> powerpoint presentation of my recent lecture on tektites.
>> Check out 'What's
>> New?' on www.tektites.co.uk.
>>
>> http://www.tektites.co.uk/whats-new.html
>>
>> Regards,
>>
>> Aubrey Whymark
>>
>>
>>
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>
>
>
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Received on Mon 21 Feb 2011 09:37:48 PM PST