[meteorite-list] Philippinites - shape formation ideas.

From: Aubrey Whymark <tinbider_at_meteoritecentral.com>
Date: Mon Nov 6 10:14:56 2006
Message-ID: <20061106103109.18800.qmail_at_web26314.mail.ukl.yahoo.com>

Hi Guys
 
TEKTITE PHILIPPINITE SHAPE FORMATION
 
I have been purchasing a large number of philippinites here in Manila. These philippinites, I have been told by my supplier, come from Baguio. Baguio is in Central Luzon (the large northern island of the Philippines) and forms highland ? with conifers growing in the cool climate. I visited this place and found no tektites (or anybody who knew what a tektite was). Here in Manila I am buying as much as I can. My supplier, who has collected for 20 years, has not got any new ones for 3 years now, and I think I have already got the best out of him. They are not that cheap and have pretty much used all my money up ? so I?ll be selling a few at some point (probably in December).
 
My observations have led me to some conclusions that differ slightly from previous articles I found on the internet (although I have not checked my references in UK). Philippinites are characterised by their ?u? grooves. These ?u? grooves only tend to develop on one side and this is what I intend to discuss. Philippinites come in a variety of shapes including ?breadcrust? forms (which look like half-soccer balls), dumbbells and tear drops, the classic ?5? grooved ?cores? and spheres. Interestingly, on average, philippinites appear larger than I had imagined. My biggest is around 360g, with many around 50g.
 
Interesting articles on the internet are:
http://www.tektitesource.com/Bikolites.html
http://www.meteorite-times.com/Back_Links/2002/November/Tektite_of_Month.htm
 
My pictures (refer to with the following text) are in the BIMS homepage:
http://tech.ph.groups.yahoo.com/group/britishandirishmeteoritesociety/photos/browse/8c74?c=
 
The observations made in ?The Tektite Source? were excellent and from what I?ve seen I fully agree with them. The observations made by Paul Harris in the meteorite times were also excellent, but I wish to argue about the anterior/posterior side. Polygonal cracks are commonly found in geology. The best example is in basaltic lavas such as the classic ?Giants Causeway? in Ireland. Polygonal cracks are caused by contraction due to cooling. The cool side of a tektite on re-entry is the posterior (in australites material solidifies on the posterior as it is cooler). My second piece of evidence is the Apollo re-entry craft (meteorites were studied for its design I believe). I note that on philippinites the smooth side is always shield-like. It is pretty similar in most specimens, but the grooved side is variably convex (and usually more convex than the smooth side). My third piece of evidence comes from the large specimen pictured. Unfortunately this did not come out
 well in the photo, so is not shown. On the ?smooth? side is an originally textured surface. But in one area it is smoothed off ? a feature I have also observed on some indochinites from Thailand. It looks as if it landed on this surface whist still hot and slightly plastic. The ?thud? flattened an area and removed any pock-marking, which exists on the rest of the rounded surface.
 
So, large philippinites form ?breadcrusts? which kind of look like half-soccer balls. On these ?breadcrusts? a smooth shield-like anterior (facing direction of travel) surface forms. On the posterior (behind) the tektite cools faster, thus forming polygonal cooling contraction cracks. These polygonal areas can crack off in flight and can leave a smaller core of about 1-4cm in size, not to mention numerous ?side? pieces. These ?cores? often have a rounded polygonal outline. These smaller tektites may of course, already have just been small. They show the classic shield-like anterior and grooved posterior. The cracks on the posterior are the same as on larger specimens but only develop as typically 5 cracks on the edge with no interior polygon developed.
 
The ?u? grooves formed due to chemical weathering along lines of weakness ? which are the cooling contraction cracks. The end result is spectacularly beautiful tektites, surpassed only by the australites.
 
I?m interested in any comment regarding this subject. Tektites have fascinated me for 15 years now.
 
Kind Regards,
 
Aubrey

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