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Banded chert or shell?


hndmarshall

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6 hours ago, hndmarshall said:

leaning toward banded chert but double checking... found a couple of these....interesting stone.

Please always include where your items were found in the first post when looking for an ID. 

While some of us are familiar with your previous items, others may not be. 

Location gives us a context from which to base our opinions.

 

It is not always apparent where items were found. 

Some people find things on vacations, or day trips, or in boxes in the basement. ;) 

 

That said, it is an interesting stone. 
I would go along with banded chert. 

 

 

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1 hour ago, Fossildude19 said:

Please always include where your items were found in the first post when looking for an ID. 

While some of us are familiar with your previous items, others may not be. 

Location gives us a context from which to base our opinions.

 

It is not always apparent where items were found. 

Some people find things on vacations, or day trips, or in boxes in the basement. ;) 

 

That said, it is an interesting stone. 
I would go along with banded chert. 

 

 

gravel load west of Houston Texas from Brazos Texas

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1 hour ago, ynot said:

Although it does have a superficial look of banded chert the grain looks to course for chert.

I think it is a quartzite.

I agree it is too grainy for chert, so some other type of layered stone. 

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everything I find is cert now I find this and I figured it was banded cert even looked it up was so sure and now its not cert......:headscratch::rofl: 

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2 hours ago, erose said:

I agree it is too grainy for chert, so some other type of layered stone. 

 

4 hours ago, ynot said:

Although it does have a superficial look of banded chert the grain looks too coarse for chert.

I think it is a quartzite.

Do not count chert out yet. The rough exterior hides the diognostic interior. The rock cannot be too grainy since the exterior has numerous curved percussion marks that indicate well developed chonchoidal fracture. (See center and right side of third photo.) Microcrystalline and cryptocrystalline forms of quartz with conchoidal fracture including chert, jasper and quartzite. Short of cutting and polishing the rock we need to see the interior. Chip a piece off for us to see and take a close up photo. My biggest question is how this was formed. Could it be a piece of wood. The interior microscopic details will tell.

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1 hour ago, DPS Ammonite said:

 

Do not count chert out yet. The rough exterior hides the diognostic interior. The rock cannot be too grainy since the exterior has numerous curved percussion marks that indicate well developed chonchoidal fracture. (See center and right side of third photo.) Microcrystalline and cryptocrystalline forms of quartz with conchoidal fracture including chert, jasper and quartzite. Short of cutting and polishing the rock we need to see the interior. Chip a piece off for us to see and take a close up photo. My biggest question is how this was formed. Could it be a piece of wood. The interior microscopic details will tell.

good idea may try it when home am at office right now

 

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I would like to compare these two pictures. There are evidently similar wrinkled patterns on the surface. Isn't it? :)

 

000_0438.JPG.8c90edf9c259980a7052be4c2792652b.thumb.JPG.4e21b68e72c0b21ad3842422188b138f.JPG5bce31fb772aa_poop5.jpg.61de2055e8f3ea92bd27e70b2cbb1479.thumb.jpg.5641d644a9d4cc12e9d7b851724ade08.jpg

comparative picture from

 

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4 minutes ago, abyssunder said:

I would like to compare these two pictures. There are evidently similar wrinkled patterns on the surface. Isn't it? :)

 

000_0438.JPG.8c90edf9c259980a7052be4c2792652b.thumb.JPG.4e21b68e72c0b21ad3842422188b138f.JPG5bce31fb772aa_poop5.jpg.61de2055e8f3ea92bd27e70b2cbb1479.thumb.jpg.5641d644a9d4cc12e9d7b851724ade08.jpg

Both show the circular percussion marks that are indicative of quartz related rocks with conchoidal fracture.

My goal is to leave no stone or fossil unturned.   

See my Arizona Paleontology Guide    link  The best single resource for Arizona paleontology anywhere.       

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56 minutes ago, abyssunder said:

I would like to compare these two pictures.

Rock 1.

Has district banding with indistinct borders.

Shows a small grain size, with differential weathering. 

Shows a conchoidal fracture with a rough granular surface.

Has no fine polish to the surface.

My conclusion is a metamorphic silica rich sandstone or coarse siltstone, hense  "quartzite".

 

Rock 2.

No visible banding.

No grain apparent, very fine grained. No differential weathering shows.

Has a distinct conchoidal fracture with a fine felted surface.

Shows a relatively high polish for a river tumbled rock.

My conclusion is a cryptocrystalline quartz rock. Does not look like any agates or jaspers I am familiar with,  nor does it look like aventurine or chrysoprase.

Therefore it should be chert or flint. Chert is the term most used on this site- so I said "chert", but it could be a few other things as well.

 

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Ok cut a piece off well actually cut part way then broke it off....also took pics up close with micro camera.

 

Sun Nov 11 20-47-57..... is the epicenter of the bands a solid spot of white.

Sun Nov 11 20-48-27 and Sun Nov 11 20-49-13....are close ups of the bands.

Sun Nov 11 20-49-29....in this one you can see very faint bars.

Sun Nov 11 20-49-35...very center no barring and dark.

last two just a few spare pics of stone...around the edges.

Sun Nov 11 20-47-57.jpg

Sun Nov 11 20-48-27.jpg

Sun Nov 11 20-49-13.jpg

Sun Nov 11 20-49-29.jpg

Sun Nov 11 20-49-35.jpg

Sun Nov 11 20-52-21.jpg

Sun Nov 11 20-52-57.jpg

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I have to agree with @ynot. It appears to be quartzite. The gradation is reminiscent of sandstone bedding. The bands appear to be folded. Folding requires a rock to be hot enough to be bent without brittlely breaking and enough pressure to cause the rock layer to squeeze. This process will turn a sandstone into a quartzite. It's not hot enough to melt it, only enough to cement it together so bands in sandstone can still be present. Chert and sandstone are both made up of SiO2 so the typical mineral tests will show the same result. You can try scratching a glass bottle with it to confirm if it is SiO2 or something else. 

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22 hours ago, hndmarshall said:

leaning toward banded chert but double checking... found a couple of these....interesting stone.

 

000_0437.JPG

000_0438.JPG

 

 

I'm confident this is banded chert.  It forms a "cortex" that can vary in crystalline density, but the conchoidal fractures are the real clue to what is inside this stone.  Interestingly, the color of the chert inside will be nothing like you see on the cortex.  I've seen many similar examples of this kind of chert in Texas.

The human mind has the ability to believe anything is true.  -  JJ

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21 minutes ago, JohnJ said:

 

I'm confident this is banded chert.  It forms a "cortex" that can vary in crystalline density, but the conchoidal fractures are the real clue to what is inside this stone.  Interestingly, the color of the chert inside will be nothing like you see on the cortex.  I've seen many similar examples of this kind of chert in Texas.

if you check above I had cut the stone and posted pics

 

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Still think it is chert...with eye protection, you could taken one of your other quartzite stones and give it an angled strike on a thinner edge to remove a flake.

The human mind has the ability to believe anything is true.  -  JJ

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Summa summarum:
The external patterns, which I wanted to compare, selected from different samples of different locations, reveal same patterns. That may exclude the possibility of shell.

Here's another comparative example:

 

5be9f07f339d8_Figure2.thumb.jpg.7ebc3aa80e85b58f764dee6deafaeaef.jpg

excerpt from W.U. Reimold & R.C.A. Minnitt .1996. Impact-induced shatter cones or percussion marks on quartzites of the Witwatersrand and Transvaal Supergroups?. South African Journal of Geology 99(3): 299-308

" We are not separate and independent entities, but like links in a chain, and we could not by any means be what we are without those who went before us and showed us the way. "

Thomas Mann

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18 hours ago, hndmarshall said:

if you check above I had cut the stone and posted pics

 

Can You post a picture that shows the cut and brake (just not so close)?

How did You cut it? Rock saw or other?

 

 

Darwin said: " Man sprang from monkeys."

Will Rogers said: " Some of them didn't spring far enough."

 

My Fossil collection - My Mineral collection

My favorite thread on TFF.

 

 

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I am cracking up!  I posted almost identical pictures about 2 weeks ago!  Top (brown) is from Netherlands- North Sea.  

“Banded” stone/Shell is from Tel Aviv- Mediterranean Sea.   

 

 

2C3535EF-AB04-413F-B7E3-DD8F981FDB46.jpeg

B223ACB2-75B7-4E5B-ABE7-726C595D181A.jpeg

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