Libyan desert glass, will the mystery ever be solved

Having just aquired my LDG specimen I have been trawling the internet for more info on this stuff.
Even though some people believe the Kebira crater could be the source of the LDG, it seems there is some debate if its even a crater, but even if eventualy its proved to be not a crater it doesnt matter because it has been speculated there was no impact at all and the LDG was formed by a airburst of a meteroid or comet, like the Tunguska event which would explain the lack of a crater, I'm happy enough to go with that theory!
However something had been bugging me, it seems to me that a lot of places are suggesting this event happened over a sandy area like the desert is today, but this happened about 28 million years ago, and i started wondering if the desert was there at all all that time ago, it could have been lush forests back then so where would all the silica have come from?
Then i found this interesting article, that explains a possible non impact origin.
[www.b14643.de]
This seems to be the most comprhensive research i have found that points to a non impact explanation, It even explains how the traces of Iridium got there.
I think a lot more research needs to be done on LDG, until then i will continue to believe my LDG is the result of a meteoric event.
Before i finish this post i have a question about some features i found on my specimen, one i think is a lot easier to explain than the other, i found several round cavities in which are embedded almost spherical opaque greyish objects, i am 99% sure these are quartz grains that have been rounded by the action of sand erosion that have found there way into the cavities, they seem to be held in place by orangey sand. I inititialy thought it might be cristobalite as i read this can be found as incluisons in ldg, and i saw some photos which showed they are spherical, and i wondered if the objects where close to the surface and got weathered out, but then i found out those cristobalite inclusions are tiny so i think i can rule that out, you can see one of the spheres in the attached photo.
the close up photo shows a strange feature that i think is harder to explain, i call it a slug! it was hard to get a decent photo as it is quite small the best i can describe it as if some molten wax was dripped on it and has enclosed some pinky orangey material similar colour to the sand in those cavities only this is entrapped within the "slug"

Jason



Edited 1 time(s). Last edit at 02/12/2011 09:49PM by Jason Evans.

[www.b14643.de]
believes that "volcanic glasses and tektites of the same origin."

Have updated the page with additional info and numerous refs.
[www.mindat.org]



Edited 1 time(s). Last edit at 02/14/2011 01:02PM by Uwe Kolitsch.

Interesting theory.

In my spare time...when I have it, I occasionally go on impact crater hunting sprees on Google Earth. Of course I can't always positively distinguish impact craters from terrestrial based geological features, but from the south wester portion of Ethiopia, to the western corner of Algeria, it seems that Africa got completely pelted, with the bulk of the features with the bulk of the features slightly north of the intersection of the borders of Chad, Sudan, Libya and Egypt. There is a well known crater field in Egypt.

If most of these features are impact craters, as to why they are still visible, I'd imagine that either there just haven't been many eroding factors, or the craters, at one point, were buried and preserved, and then unburied.

I wonder if it's also possible that a meteorite came in at such an angle, and hit such a deep pocket of sand, or sand stone, that most of the energy went into melting it and launching it up in the air, leaving not much of a trace of an impact crater. But it really isn't that there are no impact crater candidates for the origin of the desert glass, it's that there's so many.

I certainly hope it is not true that tektites and volcanic glass are of the same origin, or it could turn out that my new moldavite is nothing more than a expensive bit of obsidian!
That report i linked really does seem to suggest a terrestrial origin for LDG and hints at it being formed by hydrovolcanic processes
I shall click on the links on the ldg page here on mindat and see what more i can find out.
I still think a airburst could be the cause.

That is a compelling argument put forth regarding volcanic glasses and tektites, however I noticed that none of the data presented in the tables measures the rare trace elements found from meteoritic origin. This was conveniently left out.

According to Koeberl's theory that they are tektite origin, the zircons found in the glass were melted at 1800 C degrees, much higher than the temp of volcanic melt at around 1100 C degrees.

There is a BBC presentation called The Fireball of Tutankhamun, sometimes referred to as Tutankhamuns' Fireball, have you seen it? You can find the 10 minute excerpts on youtube , I used to have all the links (the show is about 60 minutes) but the ones I had are now dead, but I found a link to excerpt part that discusses the zircons, the other parts are out there somewhere:

[www.youtube.com]

hope you find it useful

regards,
stephanie



Edited 1 time(s). Last edit at 02/15/2011 05:25AM by Stephanie Martin.

Of course it's entirely possible that a meteorite hit a lava field.

Thanks Stephanie, i was aware of that program but only found one link for it and like you said, the link was dead, i shall now watch the youtube excerpt from the link you provided.
I thought i did see mention of how Iridium was found in the ldg from that report, it says it could eb from the molten material from the earths interior, although im not convinced by that, surely then iridium would be more common in other igneous rocks?
I wish there was some way to replicate the conditions that caused the ldg (on a small scale) i think that is the only way the mystery will be solved.
Jenna, that is a very interesting theory about a meteor strike in a lava field, a theory that seems to have been overlooked! but seems perfectly plausible to me.

Pardon the pun, Jenna you may have hit on something with that idea!

Jason if you have a bit of time you can search youtube and you should be able to find the other excerpt parts for that show.

stephanie

I found them! not on youtube though, infact iot was really annoying becuase i did find a few excerpts there, infact most of the show was on there, i think it was missing the first and last part, which i watched but that only served my need to see the complete program so i did some more looking about and found the complete set here.
[www.disclose.tv]
This is a excellent program and i found it fascinating, i watched the whole thing whilst holding my very own ldg specimen! (im odd!) its very cool to have something thats so interesting it gets its own program about it, and that has been the subject of so much scientific study.
It was pretty much conclusive about it being caused by a meteoric aerial blast, and i am certainly happy to accept that theory!
I am still interested in Jenna's theory, that is something that does seem to have been overlooked and it would be interesting if they could do more research as to what would happen should a meteorite impact a lava field, it could also explain other tektites.
I have a theory of my own which is probably very wrong but im not really a scientist and dont know the mechanics of what happens during an impact.
In the programe they mention the area could lilely have had lakes, i wondered what if one of these lakes were quite large, or maybe there could have been a shallow sea, although then i suppose fossils of marine creatures would have been found, but ok lets say there was a very shallow saline sea which might not support much in the way of large animals.
What would be the effecst of a impact or large aerial explosion over such a body of water? could it not at least explain how the glass would have cooled so rapidly?

PS, I propose Libyan desert glass be re named Egyptian desert glass as it mostly seems to be found on the Egyptian side of the border, in the program it is mostly refered to as "the glass" or desert glass, but i am sure there was one reference to egyptian desert glass. And i was thinking this before i saw the program.
Of course i doubt it will suddenly become EDG but i see no reason why it should be called libyan desert glass, i dont think there is a official name for it, its not like the IMA can have any say of the naming of such substance.
I shall call it EDG from now on!

This is a little off topic, but has anyone seen any references mentioning early human discovery/use of the glass? I'm not talking about stone-age artifacts, which seem to be locally abundant, but use as raw material in "man-made" glass. The easiest way to make glass is to include some that has already been melted once. Old-Kingdom Egypt produced some of the earliest known glass art & I have long wondered if natural Lybian glass could have got them started. I asked at the Corning glass museum (with a great Egyptian collection) and just got blank looks. RD

I would imagine it was easier just to make it using whatver processes they used back then, they would have to have melted the ldg and im not sure if that was any easier than just melting sand or whatver thay did so it would have been a waste of time to send people out to bring the Egyptian desert glass back for processing when they have a plentiful supply of sand.
Just my speculation though.

The problem with using LDG as a starting material is that it is relatively silica rich and therefor has a melting temperature of ~1700. Soda rich glasses maybe melt 500 degrees lower in temperature, so the use of cullet would start the melting process at a lower temperature, which is easier to do.

That answers it, thanks - I did not realize silica content was so high!

Thanks Jason for starting this discussion!

People ( especially "scientists" ) all have different filters to arrive at "truth."
My filters drive me toward the impact or near impact theorys.

1. High temperature -1800 degrees C. glass.
2. Formation in the glass of high temperature cristobalite spheres.
3. Shocked quartz crystals only found in impact areas.
4. Diamonds.

Those are conclusive for me.

Next Question,
What was the speed? Was this a head-on or rear end collision? Space rocks land with speeds varying from terminal velocity (200 + mph) to 120,000 mph. That varies the energy of impact over a huge range of possibilities.

What was the angle of impact? low trajectories can skip off the atmosphere or the ground. slightly higher trajectory impacts create ejecta rays down range. All high speed impacts at angles above 10 degrees result in spherical craters.

What was the objects composition? "All asteroids are high in iridium" statements after the K/T boundary discovery are bogus. Unless chunks broke off some original object, they are all different. How much iridium is found in iron meteorites?
Where do they come from? An interesting possibility is at: [apod.nasa.gov]

Apparently a "near miss" wiped out all the mega fauna including humans 12,900 years ago from California to Maine.
Check out the "Black Mat."
[www.eurekalert.org]
[georgehoward.net]

An aerial burst of an object 120 meters in diameter traveling at 20 km/second has been calculated to product temperatures up to that of the surface of the Sun. That would melt the surface with no impact crater.

30 million years is a long time to erode and break up whatever the original site looked like.

What has happened before could happen again. There may be some exciting days ahead.

Those are the facts that also make me believe it was an aerial burst, infact it is pretty conclusive! but people will always try to come up with different theorys, thats what science is!
I have an image in my head of an aerial view of Trinity site and the starburst green lake of trinitite, only a lot bigger and instead of a ugly dull green glass its full of a lovely translucent greenish yellow glass, i bet it looked quite impresive from space, especialy as the sun passes over it, i would imagine it would reflect of the surface of the fresh glass and be quite noticeable.
I still have questions about the desert glass, like why is it so different from other impact glass, it must have some connection on the target material, the rocks must have had a high concentration of silica in them, and there is a lot of silica in that desert sand but that sand wasnt there 30 million years ago, what was the geology of the area then?
I think before the glass got sand blasted into its present day form it may have resembled the muong nong type tektites
I have become obsessed by this stuff!

hi , some part of the tektites specimens found in the world have cristobalite inclusions inside them. we know the exact temperature range needed for cristobalite to crystalised and not change into tridymite.why we can't compare the temperature produce by a meteoric impact and the approximated cooling speed of the material create and send in the air by this impact ? we have two form of silica form into one specimen . we often see cristobalite into volcanic glass or quartz point like brazilian amethyst . the study of why two form of sio2 are found in the same specimen can probably be helpy to understand the formation of the impact glass . someone know if a scientist already try to recreate impact glass at smaller scale in lab by sending somes pellet (of each kind of discovered and well indentified meteorites) at the same speed than an average meteoric impact on many kind of rich silica sand or kind of fields where we can founds this tektites.by the past many test like that was made to learn how crater was made