What are these shiny black rocks?

[wildcatman71]

Last week we went to the Cave in Rock, IL area and was digging around in an old fluorspar mine....and found these. These are the only ones like this I have ever found there. Very shiny, glassy black rocks. Please let me know what I have here. Thanks!!

 

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[diggummup]

Obsidian

 

[rwsnc]

Looks a little like Anthracite coal. http://www.google.com/imgres?imgurl...mage_result&resnum=6&ct=image&ved=0CBwQ9QEwBQ

 

[Eu_citzen]

Obsidian or possibly slag can be similar in appearance.

 

[wildcatman71]

now I am really confused....it looks just like the obsidian....as well as the anthracit coal.

 

[sniffer]

put a match to it, if it starts to melt it's coal

 

[wildcatman71]

ok....held a lighter to it for a good bit....no melting whatsoever.....also....it seems too heavy to be coal, in fact it is quite heavy for the size....I havent weighed it and compared the weight to a rock of the same size....but it does seem heavier.

 

[sniffer]

see if you can take and chip a piece off it, if it fractures easy but has a sharp edge it could be obsidian
check this out
http://en.wikipedia.org/wiki/Obsidian

 

[Nashoba]

That is obsidian..If it did not melt or burn I would bet my eye teeth one it.
~Nash~

 

[DanB]

It looks like old slag glass.....kind of weathered.....there are a lot of air bubbles trapped in the glass.....I have a smelter and I am willing to bet it is old slag.....the bubbles in obsidian would appear more consistent in size ......not sporadic sized bubbles as seen in the photo....
here is a photo of my slag glass....sorry don't have more of a close up...

db

 

[wildcatman71]

I didn't buy these....I picked them up while digging around in an old abandoned rock quarry.

 

[Tuberale]

May I offer an alternative? May still be glass, though. Just not obsidian in the classic sense.

A meteorite which strikes the Earth produces ejecta from the impact site, which can melt from the pressure of the impact, but solidify while still in the air. Usually dark, glossy black, similar to obsidian. Called tektites. Try searching for images on google for tektites.

 

[Eu_citzen]

May I offer an alternative? May still be glass, though. Just not obsidian in the classic sense.

A meteorite which strikes the Earth produces ejecta from the impact site, which can melt from the pressure of the impact, but solidify while still in the air. Usually dark, glossy black, similar to obsidian. Called tektites. Try searching for images on google for tektites.

I am doubtful if he found it in a old rock quarry??

 

[uthunter]

Not a tektite.

Tektites are either a rocky or a crystal, the rocky are similar in appearance to lava rock, moldavites are a green color and are only found in one place in the world (recognized place that is). Moldavites have reportedly been found in other areas but have been found to be a desert glass or other substances (fakes).

 

[Tuberale]

Disagree, uthunter.

Tektites are known from several locales around the world. One famous spot is in Australia, but currently illegal to remove anything associated with meteorite strike (meteorite, tektite, etc) from Australia.

However, it was not always that way...

When meteorite/comet struck where silicon dioxide (quartz) was common, ejecta very possibly small pieces of black tektite.

Just as meteorites are not more common in one place or another on earth, tektites similarly can be found many places. This should not be surprising. It has been estimated that every square mile on earth receives a meteorite impact of up to a pound every 10,000 years or so. Erosion being what it is, eventually these pieces of impact-molten glass erode out of the soil and are concentrated in waterways.

 

[High Plains Digger]

Gotta agree with Tuberale, for the most part anyway. I think I had this discussion with uthunter, but maybe not. Tektites are found in numerous places in the world, but Moldavites are found in the Moldov Valley of Cezch. and are tektites. Just branded, so to speak. And I don't subscribe to the impact theory, but more of the sloughing off the meteorite theory, but there are problems with that, too.

 

[Tuberale]

Meteorites frequently shatter 50-150 miles above the Earth. The particles which strike the earth are still called meteorites, and can still usually be traced to the same original bolide.

Tektites are not parts of meteorites. They are molten ejecta from meteorite impacts which solidify while still in the air.

Chemically, tektites are the same as obsidian, also known as "natural glass."

They are not formed the same, however. At Lava Butte and Obsidian Butte in Oregon, molten silicon dioxide flowed in a volcano. That's why "streams" of obsidian can be found near Cascade volcanoes.

Another associated mineral used as a natural abrasive is pumice, which is solidified volcanic froth. Some pumice is so light it literally floats on water from trapped air pockets inside. Other minerals associated with volcanoes include basalt, aa lava, and andesite. As I live literally on the side of a volcano (Mt. Tabor, the only dormant volcano within a major metropolitan area in the world), I am very aware of andesite, basalt, pumice, and obsidian. The only naturally-occuring mineral similar to tektites are called "lava bombs" are are ejecta spewed high and wide during a volcanic explosion. When Mt. St. Helens exploded/erupted in 1980, I was only 35 miles away. It was possible with a telescope to watch continuous lightening strikes in the 30,000-80,000 foot column of smoke and ash rising from St. Helens, and if you were unfortunate to be closer than I was, you might have been struck by some of the lava bombs.

 

[High Plains Digger]

Ok, admittedly I went to school back in the time when they were only thinking about things like mitocholdrial DNA, so perhaps I am in league with the blood letters and conjurers. But I did pay attention in my geology class and I have just a short lecture that is at some odds with Tuberale.
1. If tektites are ejecta from meteorite hits, why are they all (pretty much) te same color, whether the met. hit granite, red sandstone or white limestone? And if the met. explodes in the atmosphere, how can they create molten ejecta, even with small pieces.
2. Show me a Canyon Diablo Tektite. Really. I would like to see one.
3. Obsidian is rapidly cooled lava that did not develop crystal structure. But that also is the part that I don't have a full understand of.
4. Pumice is frothy glass that is erupted from the volcano. The Son of Krakatoa (forgetting again) has put out feet and feet of pumice that has washed back into the beach.
5. Basalt is a type of lava, not a mineral. It has minerals in it.
6. Aa (pronounced AhAh, because when you walk on it, it is sharp and hurts your fee. Ah.....ah....ahAHAH.) is a form of a lava flow that is sharp and pointy. Another kind of flow is ropy and I think may be called pua pua. But they are flows, not types of lava. You don't ah ah on pua pua.
7. I don't know about andesite, but Rhyolite is a type of lava also.
8. Lava bombs are just that, expelled lava that makes a bomb with a streaming tail that forms as it flies through the air. It is the same substance as what is in the volcano and in the flow. Basalt, rhyolite, or whatever. But different from tektites. I have seen lava bombs in the walls of Hanauma Bay, and if it wasn't for the Feds and Pele, I would have smuggled one out.

So, there you have it. Maybe we should team up and get our Doctorates. And fight out opposing theories. But I will tell you, for every hole I have for your ejecta tektite theory, there is one for my streaming solidification of gasses theory. But which ever one, I don't think there is a tektite out there that one can say is rock and glass.

Anyone out there need pictures of these things? I hate to be too boring and not even offer photos.

 

[Tuberale]

Ok, admittedly I went to school back in the time when they were only thinking about things like mitocholdrial DNA, so perhaps I am in league with the blood letters and conjurers. But I did pay attention in my geology class and I have just a short lecture that is at some odds with Tuberale.
1. If tektites are ejecta from meteorite hits, why are they all (pretty much) te same color, whether the met. hit granite, red sandstone or white limestone? And if the met. explodes in the atmosphere, how can they create molten ejecta, even with small pieces.
Tuberale answers: Meteorites can explode (and often do) before they strike the ground. At that stage, they are not meteorites, but rather meteors. Only after the object has struck the earth is it called a meteorite.
2. Show me a Canyon Diablo Tektite. Really. I would like to see one.
Tuberale answers I believe Canyon Diablo was too long ago for tektites to survive till today. I think. I know the main mass is still buried underneath the crater, but at some depth. Hundreds of pieces of the meteorite were removed from the explosive force of the impact, and have been found several miles away. My uncle gifted me a small piece of meteorite recovered near Canyon Diablo. I could give a picture of that, if you like.
3. Obsidian is rapidly cooled lava that did not develop crystal structure. But that also is the part that I don't have a full understand of.
Tuberale answers Yep. Pretty much that's it. If the flow cools relatively quickly, it has no time to form crystals. Basalt is usually lava that cools over a period of years, leaving the huge crystaline structure behind. To see it, one need only look at Devil's Tower in Wyoming.
4. Pumice is frothy glass that is erupted from the volcano. The Son of Krakatoa (forgetting again) has put out feet and feet of pumice that has washed back into the beach.
Tuberale answers I have not seen pumice erupted from a volcano. I have seen pumice flows near the Three Sisters in Oregon, as well as obsidian flows nearby. But maybe we are talking the same thing here. Lava does not have to move rapidly to be a lava flow. In Oregon as in more level areas of Hawai'i, lava moves like slow pudding most of the time.
5. Basalt is a type of lava, not a mineral. It has minerals in it.
Tuberale answers You're right! Mea culpa.
6. Aa (pronounced AhAh, because when you walk on it, it is sharp and hurts your fee. Ah.....ah....ahAHAH.) is a form of a lava flow that is sharp and pointy. Another kind of flow is ropy and I think may be called pua pua. But they are flows, not types of lava. You don't ah ah on pua pua.
Tuberale answers: I am unfamiliar with pua pua. And I just asked someone who grew up on Hawai'i, and doesn't recognize the name either. I've never heard the above explanation of aa lava before. Not saying it's wrong, just never heard of it before.
7. I don't know about andesite, but Rhyolite is a type of lava also.
Tuberale answers While I am not a geologist or a vulcanologist, I believe rhyolite is a form of lava.
8. Lava bombs are just that, expelled lava that makes a bomb with a streaming tail that forms as it flies through the air. It is the same substance as what is in the volcano and in the flow. Basalt, rhyolite, or whatever. But different from tektites. I have seen lava bombs in the walls of Hanauma Bay, and if it wasn't for the Feds and Pele, I would have smuggled one out.
Tuberale answers Lava bombs pretty common around Mt. St. Helens, and I believe common near Mt. Lassen (in Northern California) as well. But bombs are ejecta (explosively ejected from a volcano usually during an eruption). The tails common to lava bombs are the trailing portions cooled by the air before the rock hits the earth again. Ejecta from Krakatoa was found hundreds of miles away, and the explosive eruption was heard either 2,000 or 3,000 miles away. (Sorry, that was a little before my time.)
So, there you have it. Maybe we should team up and get our Doctorates. And fight out opposing theories. But I will tell you, for every hole I have for your ejecta tektite theory, there is one for my streaming solidification of gasses theory. But which ever one, I don't think there is a tektite out there that one can say is rock and glass.

Anyone out there need pictures of these things? I hate to be too boring and not even offer photos.

It's OK. Many people know how to search for "lava bomb" photos on Google now. Even me.

 

[High Plains Digger]

HPD answers Tuberale's answers: (Please, don't let us bore you. Not everyone could be iterested in this discourse.)
1. That is not an answer.

2. I, too, have a Canyon Diablo, although it is an individual with full crust, not a piece. (Canyon Diablo is the Arizona Meteor Crater) Do they have meteor usage right? I can't argue terminology. And they have drilled quite deeply into the bottom of the crater to mine the iron, without finding any. Puzzling. My question is, why are craters round when most meteors or meteorites come in on a very shallow angle? Shouldn't they be oblong?

3. There are lava flows all over So. Colo and N. New Mex with the columnar "crystals" of basalt. Cool stuff because you know what you are looking at when you see it.

6. Mea culpa on the pua pua.. but there is a name for the ropy lava flows. But I rest my rep on the Aa. You go walk barefoot on an Aa flow and not say "ah...ah....ah....damn." and prove me wrong. That shows that at least one vulcanologist had a sense of humor, or perhaps none at all when he made a midnight run for the potty.

7. Me, too.

I hope someone one else has been edified from our discussion. It would be a waste if only the two of us were on this, tuberale. We could have done this on the phone and enjoyed it more.

8. We pretty much agree except that all lava bombs are ejecta but not all eject form as lava bombs. But is a non-bomb form of ejecta hits you, ouch!

I am back to offering photos of tektites, both Asian and Czech. Just in case anyone is still bored and still reading this. How did we get on volcanos, anyway?

I would love to see pumice flows (the only pumice I have in my collection came in the pocket of my stone washed jeans) and obsidian flows. The only obsidian mass I have seen is the cliff in Yellowstone. And we dug a big chunk out of the side of the road up to the top of the big cone No. of Santa Fe. The really big one with a ring road around on the top of the crater.