Any budding petrologists or geologists here? (rock ID)
Discussion
I was wandering around the Surrey hills last weekend (Crooksbury Hill) and kept finding rocks like this...
It's really heavy for its size but when I tried to look at geological maps of the area nothing like it popped up (that I could find anyway). Can anyone ID it?
Greensand kept coming up in searches for this area but it didn't look the same to me.
It's really heavy for its size but when I tried to look at geological maps of the area nothing like it popped up (that I could find anyway). Can anyone ID it?
Greensand kept coming up in searches for this area but it didn't look the same to me.
The unexpected weight of the stone that you describe immediately suggests that it contains appreciable amounts of iron. I would have thought that this is a ferruginous conglomerate, of the type sometimes known as puddingstone.
However, puddingstones are often formed of rounded pebbles, where water borne gravels are later cemented by iron rich groundwater, and the many sharp sided inclusions in your example makes me wonder.
A quick Google around (Surrey not being familiar with me as it is on the wrong side of the river!) reveals that there are indeed puddingstones in the Surrey hills area, and that these have been used in the past as building stones. They often turn up in churches, as superstitions existed about their formation and supposed magical powers. This example is in the wall of a church in Cranleigh.
![](https://thumbsnap.com/sc/xTEbQbCj.jpg[/img]</a> <a href="https://thumbsnap.com/xTEbQbCj" Target="_blank" rel="nofollow">[img]https://thumbsnap.com/sc/xTEbQbCj.jpg)
However, puddingstones are often formed of rounded pebbles, where water borne gravels are later cemented by iron rich groundwater, and the many sharp sided inclusions in your example makes me wonder.
A quick Google around (Surrey not being familiar with me as it is on the wrong side of the river!) reveals that there are indeed puddingstones in the Surrey hills area, and that these have been used in the past as building stones. They often turn up in churches, as superstitions existed about their formation and supposed magical powers. This example is in the wall of a church in Cranleigh.
While a geologist my interests were in glacial and modern sedimentation, so it was all bags of sand and buckets of mud for me! I rarely had anything to do with any bits you could actually bang together, and my ‘petrology’ as such is rudimentary.
However, I did take an interest in the Herts and Essex puddingstones once, while I was active in the Geologists’ Association, and these have tended to attract the attention of those who are on (how shall we put this) the fringes of science. There developed a notion that boulders of puddingstone were ancient way markers, a bit like the idea of ley lines. They were often found in churchyards, or built into church walls or ancient farm houses. I didn’t go for this, as the in the period it was suggested they were set up, south east England was densely forested, and as big as these rocks were, I couldn’t see how you could navigate by them.
Yet people loved to draw lines between puddingstones, forming a network the width of East Anglia. When I started looking around, it didn’t take long to find out that they were just as common off the supposed trackways as they were on them. Common everywhere, in fact, if you know what you are looking at. The lines between them are just an anthropogenic construct.
People have always had an eye for curiosities, even if they lacked the scientific knowledge to explain them.
This large puddingstone has been stood upright and mounted on a plinth. You will find loads embedded in the foundations or walls of churches, probably warding off the attentions of demons.
Of course people pick up odd looking things, just like you did. Some people clean up or polish puddingstones for ornaments.
In counties like Essex and Hertfordshire there is little exposure of hard rock, and people notice these things. Formed by iron concretion of existing sand or gravel layers, they are later exposed at the surface as softer sediment around is stripped away. It is thought that glaciers may have moved them further. From the Chilterns to Norfolk, puddingstones are typically brownish, and concrete-like in appearance. I have no experience of ferruginous concretions in Surrey, but I know there are numerous exposures of iron stones where sands have been cemented into hard veins, and as you probably know, the Weald had an iron industry in Iron Age and Roman times based on these deposits.
Which brings me back to another niggling doubt. Any location that once saw iron smelting is likely to have a lot of slag knocking about, so you must be cautious. But your example is strikingly similar to the example in the church wall I posted earlier, so I am convinced enough to stick my neck out on this one.
For a definitive answer take it to your local museum or ask the local field societies. People like that are bound to know.
However, I did take an interest in the Herts and Essex puddingstones once, while I was active in the Geologists’ Association, and these have tended to attract the attention of those who are on (how shall we put this) the fringes of science. There developed a notion that boulders of puddingstone were ancient way markers, a bit like the idea of ley lines. They were often found in churchyards, or built into church walls or ancient farm houses. I didn’t go for this, as the in the period it was suggested they were set up, south east England was densely forested, and as big as these rocks were, I couldn’t see how you could navigate by them.
Yet people loved to draw lines between puddingstones, forming a network the width of East Anglia. When I started looking around, it didn’t take long to find out that they were just as common off the supposed trackways as they were on them. Common everywhere, in fact, if you know what you are looking at. The lines between them are just an anthropogenic construct.
People have always had an eye for curiosities, even if they lacked the scientific knowledge to explain them.
This large puddingstone has been stood upright and mounted on a plinth. You will find loads embedded in the foundations or walls of churches, probably warding off the attentions of demons.
Of course people pick up odd looking things, just like you did. Some people clean up or polish puddingstones for ornaments.
In counties like Essex and Hertfordshire there is little exposure of hard rock, and people notice these things. Formed by iron concretion of existing sand or gravel layers, they are later exposed at the surface as softer sediment around is stripped away. It is thought that glaciers may have moved them further. From the Chilterns to Norfolk, puddingstones are typically brownish, and concrete-like in appearance. I have no experience of ferruginous concretions in Surrey, but I know there are numerous exposures of iron stones where sands have been cemented into hard veins, and as you probably know, the Weald had an iron industry in Iron Age and Roman times based on these deposits.
Which brings me back to another niggling doubt. Any location that once saw iron smelting is likely to have a lot of slag knocking about, so you must be cautious. But your example is strikingly similar to the example in the church wall I posted earlier, so I am convinced enough to stick my neck out on this one.
For a definitive answer take it to your local museum or ask the local field societies. People like that are bound to know.
this may be of interest if you've not already seen.
I wonder if the bit about Caesar Camp is relevant to your find?
https://www.farnhamgeosoc.org.uk/Geology%20In%20&a...
I wonder if the bit about Caesar Camp is relevant to your find?
https://www.farnhamgeosoc.org.uk/Geology%20In%20&a...
It’s not unusual for ironstone concretions to be slab-like in shape. This use of car stone in a wall at St Martha’s Hill shows plenty of examples.
There are so many ferruginous sands in the Weald, all with confusing local names, that my money is still on a naturally occurring ironstone of some kind, but like I said before, a local natural history group or museum would be the best place to ask.
There are so many ferruginous sands in the Weald, all with confusing local names, that my money is still on a naturally occurring ironstone of some kind, but like I said before, a local natural history group or museum would be the best place to ask.
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