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Shatter Cones

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#1 Marvin Jenkins

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Posted 05 June 2021 - 02:56 PM

First time posting on this section of the forum and I wanted to ask general advice about shatter cones.

There is a very slim chance I may have found pieces of a fragmented shatter cone in a small area of a ploughed field. The fragments might of of course be something entirely different.

I didn’t want to just rock up on here (please forgive the joke) and post loads of pictures saying this is what I had found. 
Anyone with general advice about shatter cones would be most welcome and if I think I maybe somewhere close I would be happy to post pictures of my finds. I am not being deliberately secretive but I am not even an amateur in geology and do not want to waste anyone’s time.

 

Marvin



#2 ShaulaB

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Posted 05 June 2021 - 03:03 PM

Is the rock anywhere near a known or suspected impact site?

Please upload a picture or two.

I have collected shatter cones when out on a field trip led by a geology professor. The site in central Missouri that we visited was suspected to be an impact structure, and then was confirmed by satellite imaging.

Try investigating the surrounding geology a bit more. A local rock club might be a great place to get an opinion.

Is there a university near you with geologists who can look at it?
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#3 jimr2

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Posted 05 June 2021 - 03:20 PM

Yes, post a picture or 2 here--I am a geologist but no expert in shatter cones--or as suggested, take it to the geology dept at a University/College, or to your state's geologic survey, if you know where they are in your state--frequently associated with a State Univ. or your state's Dept of Natural Resources, etc. Good luck and hope that is what you found!

 

-jim-


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#4 ntph

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Posted 05 June 2021 - 04:02 PM

Looking forward to seeing a photo. We have loads of shatter cones around here. The Sudbury basin is full of them. One of the best places to see them is in a rock wall face excavated for the Walmart parking lot in the south end of town! There are several good examples in the rocks about 100 meters from where I am typing this. 



#5 jimr2

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Posted 05 June 2021 - 05:18 PM

Norn,

 

Ooooohhhh, Sudbury...brings back old memories...been on geol field trips there whilst back in ol' college days from NE Ohio. Anyhow, would love to see a picture--or 2--of that rx wall at Walmart with the shatter cones in it! Please post any pics here if you have--or can get--any! Thanks!!!

 

-jim-



#6 ntph

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Posted 06 June 2021 - 10:04 AM

Here is one of the best images, not of the Walmart ones (an example of which is in the same album as this)  of a cornucopia of shatter cones. 

 

My elder son is a geologist, with a geologist spouse. They love poking around licking looking at rocks and of course love finding these. My younger son is a mining engineer turned environmental engineer who rehabs mine sites. He likes shatter cones too. 

 

Here it is hard to know what event caused them--the "original" impact, 1.8 something billion years ago or the more recent 35 million year old impact (much smaller). 

I presume it is from the older event, but have no evidence or reasoning behind it. 

 

https://www.cloudyni...-img-2869-copy/


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#7 bob71741

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Posted 06 June 2021 - 01:44 PM

Marvin - Check your local library for Kathleen Mark's book "Meteorite Craters" Book is old (1987), but still represents good info on shatter cones. If you cannot find in library, look at book resellers-prices for used book are low.

 

Here is index of topic in the book:

Shattercones.62,66.69, 112-13, 123,
124, 126, 127, 150, 154, 163. 171,
199-200, 201, 204, 222-23, 228
criterion of impact. 123, 150, 163, 199
definition of, 123
indicative of explosive shock, 112,200
at La Malbaie, 163
orientation of, 112-13, 123, 124,
200. 222
search for. See R. S. Dietz
at site of nuclear explosion, 123
at Steinheim, 61, 126. 150
at Sudbury, 222
at Vredefort, 200



#8 ColoHank

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Posted 07 June 2021 - 07:18 PM

I remember looking at shatter-cones on geology field-trips to the Serpent Mound impact site sixty years ago.  In those days, we called it cone-in-cone.  

 

Serpent Mound (the 1300-foot-long effigy) is located at the WSW margin of the chaotic structure, which is about four miles in diameter and exhibits classic impact characteristics -- a ring of depression surrounding an uplifted central rebound.  Its outline is defined in many areas by forest, as is the central uplift.  Bedrock exposed in the area ranges in age from Ordovician to Mississippian.  

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#9 Marvin Jenkins

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Posted 08 June 2021 - 02:15 PM

Thank you everyone for your replies and an apology from me for not posting any pictures. I promise I will get to it tomorrow and show you all what I have, shatter cone or no shatter cone.

Very interesting info and a wealth of sites showing just how much abuse this ball of rock has been subjected to.

Marv


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#10 Marvin Jenkins

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Posted 09 June 2021 - 08:40 AM

Finally those pictures of my rock fragments that appear to share characteristics with fragments of shatter cones I have seen on the web.

I am entirely unsure though as I have nothing to really compare them to and they may well turn out to be natural or something like fossilized wood.



#11 Marvin Jenkins

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Posted 09 June 2021 - 09:52 AM

Had some issues with file size so I had to resize one to get it on the site.

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#12 Marvin Jenkins

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Posted 09 June 2021 - 09:55 AM

Another. the box cutter is only there to show size.

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#13 lee14

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Posted 09 June 2021 - 10:37 AM

Nice pics Marvin. Microscopic examination of embedded quartz crystals for evidence of shock is generally diagnostic for suspected impact debris.

 

Lee


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#14 Marvin Jenkins

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Posted 09 June 2021 - 02:19 PM

Just a little background to the rocks if I may. I have about 50 pieces ranging from the bigger bits in the photos down to pieces smaller than a finger nail. I have found 95% of them within a fifty meter radius of one point in a farmers ploughed field. The other 5% are slightly farther out of the zone, I presume due to poughing and machine transportation. All just surface finds after the field has been worked and weathered.

 

At first I thought `amazing, looks like I am finding pieces of fossilized wood which look great as features in an aquarium. Then I started to notice that although crystalline in form the crystal structures were cone shaped. This entire area is a giant basin of Calcium Carbonate laid down from a shallow ocean millions of years ago. I am a landscape gardener by trade, 20 years right here and I have not seen anything like this. Everything here is white limestone. The area is called Quercy Blanc, Blanc being the French for white.

 

I tried to find something on the internet and tripped over shatter cones; A Google search of pictures highlighted a few similar characteristics. The obvious funnel shape of the structure. A lot of my bits are spoon shaped, curved, concave on one side, convex on the other. I will not post the picture here as it may have copyright issues but if you find a picture on Google of a shatter cone with a large water mark saying ShutterStock across it then that is a dead ringer for my fragments. Another is the picture of a piece of shatter cone with a pin with a red head laid on top for scale, again spot on.

 

I only really started to get interested in this sort of thing after buying a book about geology from a charity shop. I just can't stop looking at everything now and asking why. As part of my own investigation and the possible connection to shatter cones it turns out I live a few hours drive from the Rochouart Impact Crater. I believe study has shown it was part of a major impact of multiple bodies (fragmented) from Canada to South America.

 

Any thoughts or information one way or the other most appreciated.

 

Marv  


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#15 ColoHank

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Posted 09 June 2021 - 04:20 PM

The specimens you found could be nothing more than fragments of sedimentary concretions.  

 

Some years ago, wandering through the uplands of Colorado National Monument, I discovered some rock fragments that, to me, had a distinctly organic appearance.  I found them in the Brushy Basin member of the Morrison formation (Jurassic), the source of many dinosaur remains.  Naturally, I thought they might be dinosaur bone.  Or maybe petrified wood.

 

A lapsed geologist who long ago pursued a different career, I shared pictures of them with a more qualified geologist friend who teaches at the local university.  Not fossilized bone and not pertrified wood, he said.  They're fragments of calcareous soil nodules, aka concretions. 

 

I think my discovery bears some resemblance to the objects you found.  Look at my photos and judge for yourself

 

I'd be inclined to say that, absent any other evidence of an impact -- fractured, chaotic geologic structure underlying the area, the presence of high-pressure, high-temperature quartz poymorphs like Coesite and Stishovite, the presence of shocked quartz (you'd need a polarizing microscope and some expertise to ascertain that), tectites, and so on -- those aren't shatter cones.  Have you looked at Google Earth to see if the area where you found them looks like it might be an impact area?

 

In an earlier post, I referred to shatter cones as cone-in-cone.  That's kind of what the ones at Serpent Mound looked like -- something resembling a loose stack of ice-cream cones.

 

 

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#16 Marvin Jenkins

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Posted 10 June 2021 - 12:21 AM

Thank you ColoHank, I can see a remarkable similarity between my fragments and those in your pictures, particularly picture 3.

It is the thin horizontal banding also apparent in most of my pieces that is the clincher.

 

At least I can stop wondering and stop collecting these things, now I know they are nothing special. Ok, onto collecting pottery shards......

Marvin




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