Pictured below is one of several items I have found in my back garden. I'd like to pose the question, "is this the result of a natural process?"
For clarification this pebble is I believe flint. Worth noting are the two holes with small stones wedged in them.
I would really appreciate any comments with regard to whether the holes look like they have occurred naturally or not. Would the pebble have formed like this?
Here is a close up.
And of the crooked slit
As mentioned there are a few other similar items which possibly put this piece in context but I thought I would see how this faired and if it was OK to post more.
Once again, I would really appreciate any opinions.
Actually, I think this looks like granite, not flint. Flint doesn't "round" very well and does not contain other minerals (as it is a mineral, not a rock), which I can clearly see in the pics. This would explain the holes: they appear to be where minerals have fallen out of the rock. I can see some pretty big phenocrysts of feldspar.
Hmmm.... I am not 100%, but I am pretty sure it is not granite. I have an example of another similar on the cortex - which is possibly deceiving -and it does appear to be flint like in consistency.
Here is an example - although I "think" this has been subjected to heat?
It looks to me pretty much like a natural process. I would postulate that it is the result of either a fluvial abrasional process, such as the kind which causes potholes in some riverbeds, or perhaps some kind of glacial activity where the smaller stones have been "drilled" into the flint.
Hmmm.... I am not 100%, but I am pretty sure it is not granite. I have an example of another similar on the cortex - which is possibly deceiving -and it does appear to be flint like in consistency.
I'm still pretty sure the first example is an igneous rock of somekind. I'm sure I can see minerals within. The second example is definately flint of some kind.
As Benauld said, natural processes such as fluvial abrasion can account for such things. Tools tend to be generated by knapping as drilling into flint is extemely difficult!
Jon - let's assume that I am correct and that this pebble is the same material as the second shown - I am 100% confident that this is the case since they are two to a penny here. Possibly you are seeing small amounts of sand in some of the crevices.
Would your suggestion that minerals have fallen out of the rock still be applicable?
(Bit of background info - I am located approximately on the Reading Beds, so this and similar are either from river terrace gravels or pebble gravels??)
Again, I am concerned that the picture may be a tad deceiving - there are no phenocrysts discernable.
Benauld, bearing in mind the thickness of the stones relative to the hole depth I am trying to understand what sort of situation may occur to cause holes to be eroded in such a fashion i.e below the surface of a rounded object. Additionally the surface of the holes appears to be pitted as opposed to abraded?
Thanks once again for helping to falsify my hypothesis.
The right hand hole seems to have concentric fractures/scratches around it, the others also too, but to a lesser extent. When you say below the surface of the stones, were they found in situ? If they are moved from upstream, their orientation will have changed considerably. However, it could be some kind of suction, bringing debris from beneath the stones.
Then again, they could be artifacts of the formation of the flint nodes eroding out?
Is it just my eyes or are the 'phenocrysts' in the top picture arranged concentrically around the holes. It's got me thinking about minerals 'flowing' around garnets in certain metamorphic rocks.
I'm intrigued by this but can't spend too long looking at the pictures 'cos I'm supposed to be working! :oops:
I mentioned that the first object was possibly found in "context" and perhaps this is the point at which I ought to reveal a little more.
How about this? again I am interested in comments on the depressions.
Quote:
The right hand hole seems to have concentric fractures/scratches around it
Benauld I thought that perhaps those cracks which in places form rings could have been stress fractures? The object was found in situ in the ground... I live up on a hill and the nearest rivers are the Gade and the Colne both a little way in either direction.
al8301 I am intrigued by this response and would like to explore it further but I should mention that I have a feeling (and I am not about to check this for sure at the moment) that should the pebble be split in half we would find a consistent consistency not unlike the "flint like" material shown in my second post.
GeologyRocks
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Result of a natural process?
Wed, 02/07/2007 - 21:59Hello,
Pictured below is one of several items I have found in my back garden. I'd like to pose the question, "is this the result of a natural process?"
For clarification this pebble is I believe flint. Worth noting are the two holes with small stones wedged in them.
I would really appreciate any comments with regard to whether the holes look like they have occurred naturally or not. Would the pebble have formed like this?
Here is a close up.
And of the crooked slit
As mentioned there are a few other similar items which possibly put this piece in context but I thought I would see how this faired and if it was OK to post more.
Once again, I would really appreciate any opinions.
Thanks.
Richard
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is this the result of a natural process?
Wed, 02/07/2007 - 22:18Actually, I think this looks like granite, not flint. Flint doesn't "round" very well and does not contain other minerals (as it is a mineral, not a rock), which I can clearly see in the pics. This would explain the holes: they appear to be where minerals have fallen out of the rock. I can see some pretty big phenocrysts of feldspar.
Let's see what other folk say as well
Geologists are gneiss!!
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is this the result of a natural process?
Wed, 02/07/2007 - 22:31Thanks Jon for getting the ball rolling.
Hmmm.... I am not 100%, but I am pretty sure it is not granite. I have an example of another similar on the cortex - which is possibly deceiving -and it does appear to be flint like in consistency.
Here is an example - although I "think" this has been subjected to heat?
Thanks again.
Richard
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is this the result of a natural process?
Thu, 02/08/2007 - 10:27Hi,
It looks to me pretty much like a natural process. I would postulate that it is the result of either a fluvial abrasional process, such as the kind which causes potholes in some riverbeds, or perhaps some kind of glacial activity where the smaller stones have been "drilled" into the flint.
Ben.
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is this the result of a natural process?
Thu, 02/08/2007 - 10:45Hmmm.... I am not 100%, but I am pretty sure it is not granite. I have an example of another similar on the cortex - which is possibly deceiving -and it does appear to be flint like in consistency.
I'm still pretty sure the first example is an igneous rock of somekind. I'm sure I can see minerals within. The second example is definately flint of some kind.
As Benauld said, natural processes such as fluvial abrasion can account for such things. Tools tend to be generated by knapping as drilling into flint is extemely difficult!
Geologists are gneiss!!
Rank:
Contact:
is this the result of a natural process?
Thu, 02/08/2007 - 12:32Thanks for the feedback.
Jon - let's assume that I am correct and that this pebble is the same material as the second shown - I am 100% confident that this is the case since they are two to a penny here. Possibly you are seeing small amounts of sand in some of the crevices.
Would your suggestion that minerals have fallen out of the rock still be applicable?
(Bit of background info - I am located approximately on the Reading Beds, so this and similar are either from river terrace gravels or pebble gravels??)
Again, I am concerned that the picture may be a tad deceiving - there are no phenocrysts discernable.
Benauld, bearing in mind the thickness of the stones relative to the hole depth I am trying to understand what sort of situation may occur to cause holes to be eroded in such a fashion i.e below the surface of a rounded object. Additionally the surface of the holes appears to be pitted as opposed to abraded?
Thanks once again for helping to falsify my hypothesis.
Richard
Rank:
Roles:
Contact:
is this the result of a natural process?
Thu, 02/08/2007 - 12:56The right hand hole seems to have concentric fractures/scratches around it, the others also too, but to a lesser extent. When you say below the surface of the stones, were they found in situ? If they are moved from upstream, their orientation will have changed considerably. However, it could be some kind of suction, bringing debris from beneath the stones.
Then again, they could be artifacts of the formation of the flint nodes eroding out?
Ben.
Rank:
Contact:
is this the result of a natural process?
Thu, 02/08/2007 - 14:00Is it just my eyes or are the 'phenocrysts' in the top picture arranged concentrically around the holes. It's got me thinking about minerals 'flowing' around garnets in certain metamorphic rocks.
I'm intrigued by this but can't spend too long looking at the pictures 'cos I'm supposed to be working! :oops:
Rank:
Contact:
is this the result of a natural process?
Thu, 02/08/2007 - 18:13I mentioned that the first object was possibly found in "context" and perhaps this is the point at which I ought to reveal a little more.
How about this? again I am interested in comments on the depressions.
The right hand hole seems to have concentric fractures/scratches around it
Benauld I thought that perhaps those cracks which in places form rings could have been stress fractures? The object was found in situ in the ground... I live up on a hill and the nearest rivers are the Gade and the Colne both a little way in either direction.
al8301 I am intrigued by this response and would like to explore it further but I should mention that I have a feeling (and I am not about to check this for sure at the moment) that should the pebble be split in half we would find a consistent consistency not unlike the "flint like" material shown in my second post.
Richard
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is this the result of a natural process?
Thu, 02/15/2007 - 07:27My guess is that it's flint and the holes are trace fossils such as sponges.