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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[Clay Diggins]

Wow fulgerites? Tektites? maybe but not.

It's common slag glass. It has all the signs.

For those that believe in obsidian in Illinois - I've got a bridge to sell you. There is no (zero) obsidian in Illinois or anywhere east of there. The entire east coast is devoid of obsidian. Look up devitrification to see why.

 

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[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

 

[Arid-Zone-A-seeker]

Volcanic glass, Obsidian, comes in many different forms, from the size o the pieces I would bet it is rail bed ballast.
What kind of quarry is it?

 

[rock]

With the bubbles showing in them I would go with slag. Although I dont know of any others with bubbles. Did your MD pick them up? Slag sometimes is detected as metal on your MD.

 

[Ponchosportal]

Slag

 

[Ponchosportal]

As I said ...... to me it is obviously SLAG (bubbles, lineation's, glassy appearance, hardness in excess of 6.5).

Take your materials to a local rock and mineralogy club and they will be happy to tell you what you have found.

There is no reason to be confused further at this point. Take it to a local club!

Please report back to us what the club tells you.

 

[JTJones]

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

Was metal detecting in my back yard and I found where there is a ton of this. I've found some older artifacts around that area and there's a foundation sort of like there may have been a barn or something there. Perhaps someone was smelting?

 

[Lygore]

I vote slag glass. Especially if it is heavy with a bunch of bubbles in it. You could try to see if a strong magnet sticks to it, as they sometimes do. Typical slag glass also sets off a metal detector if you sweep it over the sample.

 

[ToddsPoint]

Like Clay said, there are no natural obsidian outcrops in IL. However, obsidian has been found in IL on Indian campsites. The material was tested and the source for nearly all samples was the Glass Buttes in WY. Another sample tested revealed the source in ID. All of the samples were obtained from middle woodland Hopewell sites. Here’s a drawing of some of the obsidian artifacts found.

 

[Red-Coat]

It's common slag glass. It has all the signs.

For those that believe in obsidian in Illinois - I've got a bridge to sell you. There is no (zero) obsidian in Illinois or anywhere east of there. The entire east coast is devoid of obsidian. Look up devitrification to see why.

Agree with slag glass, and that there is no obsidian in Illinois.

What I say below is intended more as a clarification of there being no obsidian on the East Coast rather than a contradiction of what you said, since there are sources within about 120 miles of the coastline, but they’re minor.

Almost every lightweight ‘geological reference source’ (and many authoritative heavyweight sources) trot out that obsidian is not found in the Eastern United States… often expressed as “doesn’t occur naturally east of the Mississippi River”.

The rationale for the statement is that obsidian readily weathers and hydrates to form the brownish-grey opaque mineral “perlite” and it typically only takes a few million years for this to happen ['devitrification', as you said]. Given that there hasn’t been volcanic activity on the eastern side of the continent within that time, there should be no obsidian remaining and it’s generally assumed that the Native American artefacts made from it found in eastern areas were the result of trading (of material) from outside the area.

That’s only a partial truth. Obsidian can and does survive a lot longer than that, but with most specimens being younger than 50 million years and nothing has been found that’s older than 66 million years. However, the geological record suggests that there should be no magmatic flows in the eastern parts of the USA from which obsidian could have formed within the last 200 million years.

That’s now known to be untrue, notably for Virginia. The state has two ‘young’ volcanoes in the Appalachian Mountains: Mole Hill and Trimble Knob. Both of them are less than 48 million years old and exist today as the heavily-eroded necks and remnants of the interior of primeval volcanoes. They do nevertheless have the remains of gaseous vents within which there is still unweathered obsidian, first identified and documented by geologists in 1899. A few of the obsidian artefacts found in Virginia have definitively been attributed to these sources, so ancient people must have discovered them. The other possibility is that the Smith and Dan Rivers which originate from the Blue Ridge and Appalachian Mountains carry occasional pieces of obsidian from these sources into the Piedmont along the NC/VA border and that’s where many of the obsidian artefacts have been found. These tools also typically date between 2,000 – 10,000 BC, which is well before trading networks are known to have existed. The trade in lithics was extensive during the Woodland Period but doesn’t seem to predate 100 BC (Hopewell Culture).

Recent research suggests that the East Coast is not a volcano-free “passive margin” but actually a “passive-aggressive margin” that saw volcanic activity much more recently than originally believed and, although its volcanoes are now extinct, things are still rumbling below the surface. That’s the reason for the 5.8 magnitude earthquake centred near Mineral, VA in 2011. Mole Hill and Trimble Knob are believed to be part of a ‘swarm’ of volcanoes that co-existed, but the only readily recognisable ones today.

 

[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~

 

[wildcatman71]

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