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James Hunt
Joined: 09 May 2016
Posts: 7
Location: Wiltshire
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 Posted: May 13, 2016 06:17 Post subject: Re: Could this be a very rare limestone shatter cone from the UK? |
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| 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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kushmeja
Joined: 28 Jul 2014
Posts: 244
Location: New Jersey
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| Posted: May 13, 2016 07:05 Post subject: Re: Could this be a very rare limestone shatter cone from the UK? |
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| 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
Joined: 09 May 2016
Posts: 7
Location: Wiltshire
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| Posted: May 18, 2016 20:01 Post subject: Re: Could this be a very rare limestone shatter cone from the UK? |
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| 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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James Catmur
Site Admin
Joined: 14 Sep 2006
Posts: 1482
Location: Cambridge
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| Posted: May 19, 2016 00:52 Post subject: Re: Could this be a very rare limestone shatter cone from the UK? |
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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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