FMF - Friends of Minerals Forum, discussion and message board

[Fergus McConnell]

Hello! Firstly, I apologise if what I have found is entirely mundane. It caught my eye when exploring the bank of a river in Perthshire, Scotland. I am neither a mineralogist or geologist, but I found it intriguing.

From my own research, I have supposed that it is some sort of septaria. The band around the rock appears to be rust.

I would love to know how something like this formed and what is it comprised of.

I'm so sorry in advance if it's just a boring chunk of stone! Many thanks.

Fergus

[lluis]

Hi, Fergus

I am chemist, not mineralogist nor geologist (just a collector of minerals from my very 8 y.o.... and now I am somehow old... :-( )

For piece, it looks to me as man shaped piece that was hung with a wire of iron/steel.
To do what, no idea. But at least it is consistent with shape (it looks to me as if it was designed in a heart shape, like the heats of Christ with flames over used in catholics (and maybe any other branch.....). Just that I do not think that Catholics are a big crowd in Scotland....

That is the pity of when something is found and no history has been preserved... It could be all and be done by anyone..... :-(

With best wishes

Lluís

[James Catmur]

My first view was also 'man-made'. How about a boat anchor or fishing net sinker? If it was on the banks of a river that might be possible.

Pop into the Hunterian and see what they think

[Pete Richards]

I'll offer an opposing view. I think this is a piece of metamorphic rock - probably gneiss. It has a vein in it of some other material with a lot of iron in it - maybe an iron carbonate. It broke off of the bedrock it was part of, and was tumbled in the river into this rounded shape. The vein is subject to chemical weathering, so it has developed into a depressed ring. To some extent, it creates a plane of weakness that contributes to loss of rock mass, especially on the top part where the rock is thinner. The layering of the rock suggests that it is weaker parallel to the layering than across it, and it would be vulnerable to spalling off along that direction.

Mark Twain said: "Geology is a wonderful science. One gets so much conjecture from so few facts!" Perhaps that is true, at least in this case!

[Fergus McConnell]

The Hunterian is a good idea. I thought it was man made myself. But no matter how much I scrub at it, there is only rust. Also, the ring is uninterrupted. Here's another photo

[Fergus McConnell]

Fantastic insight, Pete. I had quickly realised the ring could not be man made. The fact the top part was smaller than the lower portion was intriguing, but I couldn't intelligently explain it

Thanks for that. I think I've found a new hobby.

I should have perhaps made this clearer; the river is too shallow for even a kayak. It was in close proximity of a very old bridge. Other than that, the nearest civilisation was a very long distance away. I would say that fishing or mooring devices are out of the question. Still a chance it is from the construction of the bridge, although the bridge is comprised of a very different stone

[James Catmur]

I now tend to agree with Pete. In that area, you often find thin veins running through the rock.

You need to start hunting agates in the rivers! That is fun. Have a look at

https://blog.nms.ac.uk/2018/12/19/what-are-agates/

Perthshire and Fife are good areas, or head south into Ayrshire. Once you get the bug you may never stop.

[James Catmur]

A Scottish agates from my collection

[SteveB]

Certainly an interesting talking piece full of possible What Ifs. Some form of anchor is what I was also thinking, bit small for boat but good for mooring lobster pots or fish traps. How does the rock layering line up across the iron band? Its typical for the layers to be shifted when cracking occurs contrary to the layering plane for new material to be forced in. It could also possibly part of an old statue I guess, part of an earlier bridge at the location that was replaced by current one? I think identifying the rock definitively will give you a starting point to research local quarries that yielded such rock and where is was used.

[Kevin Schofield]

Hi Fergus,

given that you found the rock in a Perthshire stream, you were close to or in the metamorphic complex of the central Highlands. That makes it very likely that this is a metamorphic rock associated with the heating around the granite intrusions of the highlands where the 19th century geologist George Barrow first described the mineralogical changes in rocks moving from adjacent to the intrusion to the furthest reaches of the metamorphism which are now (funnily enough) termed the Barrovian Zones. Google for details :-).

Anyway, that makes it likely that the rock itself is a schist, which is a rock recrystallized under heat and pressure. Going out on a limb and squinting at the second of the two pictures it is possible that some of the dark shiny minerals on the exposed faces are biotite mica, biotite being the "signature mineral" outermost, coolest Barrovian zone which, happily enough, extends through central Perthshire. That being the case, it's a local rock.

As for the relatively soft iron-rich band...please see the prior suggestions of my fellow FMFers!

Good luck with your newly-chosen hobby. Scotland is a very fine place to indulge it!