[meteorite-list] Tektite Presentation

From: Aubrey Whymark <tinbider_at_meteoritecentral.com>
Date: Tue, 22 Feb 2011 02:12:23 +0000 (GMT)
Message-ID: <858614.69312.qm_at_web28508.mail.ukl.yahoo.com>

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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Received on Mon 21 Feb 2011 09:12:23 PM PST