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Could this be a very rare limestone shatter cone from the UK?
  
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James Hunt




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PostPosted: May 11, 2016 19:07    Post subject: Could this be a very rare limestone shatter cone from the UK?  

Hi All,

Was hoping for some help in identifying what this rock is made of? I think it is made of limestone. Any help would be greatly appreciated. I was planning on taking it to the national history museum in London but would prefer not to make a fool out of myself hence my polite request.

The rock feels very dense and for such a small specimen and weighs in at 14 grams. I'd simply love it to be a shatter cone but perhaps the knowledgeable folks on here can share their knowledge and experience with minerals. The rock does not respond to a magnet for what its worth!

I have more photos should anybody require them. Many thanks for your time

James



upright close web.jpg
 Mineral: lime
 Locality:
Amesbury, Wiltshire, South West England, England / United Kingdom
 Dimensions: 2cm x 1cm
 Description:
check out the striations.
 Viewed:  20925 Time(s)

upright close web.jpg



cone top close upweb.jpg
 Dimensions: 2cm x 1cm
 Description:
top of cone
 Viewed:  20927 Time(s)

cone top close upweb.jpg


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James Hunt




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PostPosted: May 11, 2016 19:23    Post subject: Re: Could this be a very rare limestone shatter cone from the UK?  

Wanted to add an extra photo showing more of the sides to the cone


2990web.jpg
 Mineral: lime
 Locality:
Amesbury, Wiltshire, South West England, England / United Kingdom
 Dimensions: 2cm x 1cm
 Description:
a different angle with more clearly defined white markings
 Viewed:  20891 Time(s)

2990web.jpg


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kushmeja




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PostPosted: May 11, 2016 20:01    Post subject: Re: Could this be a very rare limestone shatter cone from the UK?  

It definitely doesn't appear to be limestone, but rather a metallic mineral. Possibly goethite or hematite with a limonite coating. That would explain the density as well. Without doing some basic tests it's difficult to tell for sure
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Dale Hallmark




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PostPosted: May 11, 2016 20:05    Post subject: Re: Could this be a very rare limestone shatter cone from the UK?  

If you have a ceramic wall tile see if it will leave a colored streak on the back.

Dale
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James Hunt




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PostPosted: May 11, 2016 20:19    Post subject: Re: Could this be a very rare limestone shatter cone from the UK?  

Thanks for the swift and informative reply. I'm a rank amateur I must confess and I'm about to set about googling the minerals you mentioned. The reason I thought it may actually be limestone is because of the striking resemblance to the Sudbury Basin shatter cone find in Ontario. Apparently that stone is/was limestone before being subjected to impact shock waves of a giant meteorite


shatter cone from Sudbury Basin Ontario.jpg
 Mineral: limestone
 Locality:
Bennett Lake area, Bennett Township, Rainy River District, Ontario, Canada
 Dimensions: 2cm x 1cm
 Description:
the markings and appearance look very similar to my find
 Viewed:  20818 Time(s)

shatter cone from Sudbury Basin Ontario.jpg


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Pete Richards
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PostPosted: May 11, 2016 20:19    Post subject: Re: Could this be a very rare limestone shatter cone from the UK?  

You can test if it is limestone by putting a small amount of acid on it and see if it fizzes vigorously, though a bit of lime crust on some other mineral might deceive. I think of two possibilities. One, it is a conical piece broken out of a spherical clump of crystals with a radial structure - the texture of the top view and the color suggest it might be pyrite partly altered to goethite.

Two, it is a piece of a "cone-in-cone" structure, which is a structure that develops in sedimentary rocks, typically in limy silts I would say. I don't know exactly how it develops, but one winds up with a rock layer composed of cones like this nested together, some up and some down. Usually the tops of the cones are relatively flat.

The acid test, the streak test already mentioned in a previous post, and an estimate of the density should allow you to distinguish between these two possibilities. I rather doubt that it is a shatter-cone, unless the area where you found it is known to be impacted by some explosive event - either a meteorite impact or a "crypto-volcanic" explosion. Don't know but what that latter kind of event may be totally discredited by now.

A bit later: this post of mine crossed with your second message. It would be nice to see that newly-posted piece end-on, but presumably you got it from the web so this may not be possible. Proximity to an impact site increases the possibility of it being a shatter cone, but I am still doubtful. Impact sites have some characteristics such as high-pressure, low-temperature minerals that would be included in your specimen, but this gets very technical very quickly!

It is also possible that the image of a shatter cone that you posted may not really be that at all. How authoritative are the posting and the poster?

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Joseph DOliveira




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PostPosted: May 11, 2016 20:51    Post subject: Re: Could this be a very rare limestone shatter cone from the UK?  

Here is a picture of a large shatter cone from the Sudbury basin, the point of the cone is missing. Shatter cones in the Sudbury area typically occur in metasedimentry rocks (quartzite). I think your specimen as it appears in the picture, is a radiating set of crystals. Hope this helps.

Joseph
At home in the Sudbury Crater



IMG_2744.JPG
 Mineral: Shatter Cone in Quartzite
 Description:
Sudbury, Ontario, Canada
30cmx21cmx8cm
 Viewed:  20803 Time(s)

IMG_2744.JPG



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James Hunt




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PostPosted: May 11, 2016 21:35    Post subject: Re: Could this be a very rare limestone shatter cone from the UK?  

Here is another angle of my find alongside the rotated Sudbury shatter cone. I stumbled across the shatter cone picture from the Daily Mail newspaper by chance after searching countless images. The Mail are hardy the beholders of truth and justice I will give you that! Cant post the link as spam filter blocked me. Google daily mail and shatter cones.

I actually live and found this stone in close proximity to Stonehenge monument and Porton Down military complex. Porton Down is the weapons dump for the British army. They have had a history of nuclear experiments and tests in the 1950's . Why somebody would leave the shatter cone 3 miles away is mystifying and unlikely to me hence, why I'm coming down on the side of the meteorite option. The stone could have been formed elsewhere. People have been bringing foreign objects to Stonehenge for thousands of years.

Until two weeks ago I'd never even heard of shatter cones. So a brief synopsis of what I have learnt so far from Press, message boards and academic studies that I have struggled thru on shatter cones. Shatter cones are formed in impact sites/structures.



* There are only 181 recognised impact structures (i.e. craters) that have been officially agreed upon and catalogued globally. One third of that 181 are under the sea. leaving only 121 on land and accessible


* In order to create a shatter cone a minimum force of 300 mega tons of nuclear power is required. It can only be created via a nuclear explosion or by a meteorite striking earth with that force. Scientists have calculated that the earth will on average be hit every 227000 years by an asteroid or meteorite bearing that force.


* The impact at Sudbury was estimated to have taken place 1.8 billion years ago and left an impact crater 65km in diameter. Pre mining there was no obvious depression in the landscape and over millions of years the crater was filled.. Although controversial there are accepted as a definitive indicator of an impact structure alone without any further evidence.

* The markings on the stones are called striations. The frequency of the striations and the distance in between the striations can be used to calculate the size of the force required to create the structure by astrophysicists


*The stone is formed in the bedrock by below apex of the impact explosion. It can be formed as low as 3000 feet below the surface, so the stone at Stonehenge had to of been mined or bought there?


*There has never been a shatter cone found in the UK. Compared to the rest of Europe we have an appallingly low numbers of meteorite finds. This is largely dues to our wet climate and rich soil that helps corrode anything that makes it thru the atmosphere.



shatter cone from Sudbury Basin Ontario.jpg
 Description:
Sudbury Basin
2cm x 1cm
rotated view of limestone shatter cone from sudbury
 Viewed:  20784 Time(s)

shatter cone from Sudbury Basin Ontario.jpg



3028web.JPG
 Locality:
Amesbury, Wiltshire, South West England, England / United Kingdom
 Dimensions: 2cm x 1cm
 Description:
comparative angle
 Viewed:  20784 Time(s)

3028web.JPG


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Tom Tucker




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PostPosted: May 12, 2016 00:12    Post subject: Re: Could this be a very rare limestone shatter cone from the UK?  

I've seen a number of shatter cones from "impact structures" in Missouri. Your sample looks nothing like them, but rather appears to be a broken section of a radiating pyrite nodule or concretion. It's not a shatter cone.
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PostPosted: May 12, 2016 00:51    Post subject: Re: Could this be a very rare limestone shatter cone from the UK?  

James Hunt, have you done any of the above mentioned tests? can you share the results with us? Take the word shattered core out of your vocabulary until you have actually done the tests they have suggested otherwise you are just wasting these peoples time just like you could be wasting the museums time.

The biggest mistake one can make while attempting to identify something is having set your heart on it being something it is possibly not. Get back to a neutral position where the stone is nothing but an unidentified piece of stone and then move forward attempting to positively identify this unknown stone, no prejudice.
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PostPosted: May 12, 2016 01:35    Post subject: Re: Could this be a very rare limestone shatter cone from the UK?  

Hi James, I cannot blame you for your conclusions as the similarity of the 2 specimens is striking. As it has been said, the 'internet' specimen may not even be a shatter cone. Whatever, I find the topic interesting.Waiting for some tests from you.
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Bob Carnein




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PostPosted: May 12, 2016 10:19    Post subject: Re: Could this be a very rare limestone shatter cone from the UK?  

I agree with Tom Tucker--looks like a fragment of a pyrite concretion to me.
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James Hunt




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PostPosted: May 12, 2016 17:31    Post subject: Re: Could this be a very rare limestone shatter cone from the UK?  

Pierre Joubert wrote:
Hi James, I cannot blame you for your conclusions as the similarity of the 2 specimens is striking. As it has been said, the 'internet' specimen may not even be a shatter cone. Whatever, I find the topic interesting.Waiting for some tests from you.



Thanks for your interest Pierre. As per your request, please see listed below my test results;

Ceramic scratch test - The stone leaves a pretty clear brown mark as you can see from the attached photos taken in sunlight. From what I understand, this rules out a hematite or magnetite as they leave red and black marks respectively. Could this then be the result of a limonite coating as suggested earlier on in the thread?

Stainless steel knife - When scratching the stone against a decent quality stainless steel knife it leaves a scratch on the blade. I was surprised by this. Please see the above photograph. The stone itself is completely unmarked as a consequence. I also used the knife to try and scratch the stone but to no avail

Jewellery file - definite fine scratches on the file from the stone and again no mark on the stone. If you look closely at the triangular section it was unmarked before coming into contact with the stone.

Glass - There are no markings on the either the glass nor the stone despite using a reasonable amount of force on the glass.

Hopefully the above can help eliminate a few more minerals and get closer to a positive ID



marksonceramic1.JPG
 Description:
ceramic tile test
 Viewed:  20511 Time(s)

marksonceramic1.JPG



stainlesssteel1.JPG
 Description:
knife scratch
 Viewed:  20490 Time(s)

stainlesssteel1.JPG



jwelleryfile1.JPG
 Description:
 Viewed:  20485 Time(s)

jwelleryfile1.JPG


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Reinhardt van Vuuren




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PostPosted: May 13, 2016 01:15    Post subject: Re: Could this be a very rare limestone shatter cone from the UK?  

Now we're getting somewhere, thank you James, Hardness can be a tricky test and one easily reports false positives. There is, however, one part of your test that is quite accurate and this is your streak, you reported that the stone left a brown streak. On my screen it almost looks like a reddish brown, but that could just be my display among many other things. What this test has told me is two things the stone has a colored streak and it has a hardness bellow 7. Otherwise no streak would be reported.

Do you have any acids (pool acid) or something like that? so we can see if the specimen fizzes on contact with the acid (my bets are yes it does fizz)

Also if you could do a basic Specific Gravity test using a pocket scale some water and a string of cotton. first weigh the stone dry on the scale. Write this value down. Now remove the stone and place a small container with water (enough to submerge the stone in without touching the bottom of sides of the container) on the scale and press the tare button (zero it, if your scale doesn't have that turn the scale off put the water on and turn the scale back on) now tie a piece of cotton thread to the stone so you can suspend it in the water. Make sure there are no air bubbles on the stone and that the stone is fully submerged without touching the bottom or sides of the container. This will give you a lower number. Do this wet part of the test 3 times to make sure it is accurate and take the average value of your wet test and divide the wet weight into the dry weight so say 20 grams dry divided by 2 grams wet = a specific gravity of 10. Report the results of the test back here.
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PostPosted: May 13, 2016 01:27    Post subject: Re: Could this be a very rare limestone shatter cone from the UK?  

James, the reddish-brown (or brownish-red) streak you obtained is quite common for hematite. I don't see any scratch on the knife blade or file. When you have done a scratch test, rub the 'scratch' with your finger and then inspect it with a 10x hand lens to see if it really is a scratch or just powder from the test stone.
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James Hunt




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PostPosted: May 13, 2016 06:17    Post subject: Re: Could this be a very rare limestone shatter cone from the UK?  

Duncan Miller wrote:
James, the reddish-brown (or brownish-red) streak you obtained is quite common for hematite. I don't see any scratch on the knife blade or file. When you have done a scratch test, rub the 'scratch' with your finger and then inspect it with a 10x hand lens to see if it really is a scratch or just powder from the test stone.


Hi Duncan,

In answer to your questions. The camera appears to have affected the colour in the image. As previously stated above, I took the image in sunlight to try and negate this.also managed to get two others to verify that it was brown in colour prior to my posting. Whilst researching Limonite I came across this "Limonite is relatively dense with a specific gravity varying from 2.7 to 4.3.[6] It varies in colour from a bright lemony yellow to a drab greyish brown. The streak of limonite on an unglazed porcelain plate is always brownish, a character which distinguishes it from hematite with a red streak, or from magnetite with a black streak" Does this help us with the ID?

With regards to the scratch test, The photos that I have include are actually after I cleaned off the "brown" markings from both objects. I fully appreciate that online photos are notoriously difficult to decipher but I'm very confident that the marks on the knife in particular are fine scratches. I also took pictures with the brown marks before I cleaned both objects. Hopefully this will provide a little more information for any interested parties out there
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PostPosted: May 13, 2016 07:05    Post subject: Re: Could this be a very rare limestone shatter cone from the UK?  

According to your scratch test results, you're saying that it scratches the knife and file, but not glass. That shouldn't be possible, because glass is softer than both the knife and file. Based on the pics, it doesn't appear that the knife or file are scratched, but rather it appears that some material rubbed off the stone.
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James Hunt




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PostPosted: May 18, 2016 20:01    Post subject: Re: Could this be a very rare limestone shatter cone from the UK?  

kushmeja wrote:
According to your scratch test results, you're saying that it scratches the knife and file, but not glass. That shouldn't be possible, because glass is softer than both the knife and file. Based on the pics, it doesn't appear that the knife or file are scratched, but rather it appears that some material rubbed off the stone.



Thanks again for he input. For those interested I managed to get a positive ID courtesy of the national history museum in London. They took an interest on account of the proximity of the find to the Stonehenge monument.

It's part of an oxidised (rusted) marcasite (FeS2) nodule originally from the Chalk underlying Salisbury Plain - about 85 million years old. The pyramidal crystal ends and the linear fibrous texture are a give away (plus being on Salisbury Plain)

Pre the invention of metal marcasite was used as a strike alight with flint to create fire. The stone on stone method. Whilst pyrite is commonly found on the plain marcasite is for more scarce and was prized for its fire lighting abilities in prehistory. There is a fascinating chapter on marcasite in "Pyrite a history of fools good" on google books.

Interestingly, it has a moh scale rating of up to 6.5 so looks like my amateur attempts at scratching the metal file may have actually been spot on after all unlike my brash hopes of having found a shatter cone!
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PostPosted: May 19, 2016 00:52    Post subject: Re: Could this be a very rare limestone shatter cone from the UK?  

James

Thanks for your update on the find. It is good that you found the answer and now know what it is.
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