[meteorite-list] Largest Crater in the Sahara Desert and LDG

[MexicoDoug at aol.com]

Norm L. writes:

<< Where is the dividing line between impactite and
 tektite?  I'd like to hear what others may understand,
 but my impression is that it fundamentally hinges on
 distance the glassy material is ejected from the
 crater.  Material found only in and immediately around
 the source crater is impactite.  Stuff blasted tens to
 hundreds of km or more crosses the definitional
 boundary into "tektites".
 
 If this is the criterion, LDG was already home free  >>

Hola Norm, yet again here's another one of those awkward definitions that 
when overyly analyzed starts falling apart.  I think the distance criterion is 
not THE criterion, but rather a tektite differs from an impact glass in that the 
tektite has actually been exposed to general conditions of enough kinetic and 
thermal energy to create a greater melt uniformity where the original 
impactor has transmitted that energy "cleanly", and in such a great quantity that the 
energy is also enough to propel tektites into the upper atmosphere and have 
them re-enter ablating like meteorites.

These are a bunch of hand-waving concepts, but as we know, it seems the one 
factor that really distinguishes "tektites" is the low water content.  LDG's 
have at least 5 times the typical water content of the cleaner tektites, and 
they contain inclusions including those of the impactor, and aerodynamic shapes 
are not really known I believe.

In fact the water content of LDG's at the low end of 5 times the amount of 
the cleaner tektites actually goes practically as high as obsidian.  They don't 
usually look very aerodynamic and they have meteorites inside them.  They 
deserve some distinction, they are dirty glass.  Now all of this about water 
content might be just an academic distinction, except for one exception.  One of 
the greatest mysteries of tektites is derived from the mystery of exactly what 
physical laws were twisted to get that low water content and this more than 
anything else is the criterion as much as the mystery.  Plus they are generally 
clean (OK, they have smalled fused cuartz. etc., but there there tends to be a 
bimodal distribution between clean tektites and impact glasses as far as 
inclusions = so far you have clean ones and dirty ones)  Please don't bring up 
layered tektites I don't want the definition system to fail even more...

But practically speaking, you would have to be right that there is a 
continuum, just like in the definition of a planet, etc., the world tends towards 
complexity just when you get it all figured out...and soon we will come to know of 
the impektite that bridges tektites, water and all, with LDGs and other 
impact glasses.  Better yet how about just saying they are all impact glasses - 
which they are no matter who starts talking about flying - and that tektites just 
had a higher energy/diffusion/flux melt event which is witnessed in the 
record by water content...If cats could only talk they could tell us how long we 
have erred on visible light as they see into the near UV, don't they?  What's 
the use of going at it with a cat over the definition of "visible light"?:)

My 2 centavos...Doug