On our fossil hunting adventure yesterday we came across this odd looking rock (yes I thought it was a turtle) It was found in the Annick river bed (SW Scotland) https://www.google.co.uk/search?biw=1024&bih=615&q=septarian+nodule&spell=1&sa=X&psj=1&ei=Hd5TU-__G-eh0QXY-YCQAw&ved=0CCYQvwUoAA
Quite right - septarian nodule.
They are sometimes mistaken for turtles at first sight, often without really looking that similar (to my eye). Yours does have a hint of the right overall shape, though - so I'd let you off! [smiley]
Please explain this to Leon.
...I cannot be sure of its age because the rock could be local or it could have been transported a long distance by glaciers.
Assuming it is local, and looking at a geological map of the area, it is probably from the Middle or Lower Coal Measures Formations, which comprise sedimentary rocks about 311 million years old (Carboniferous period).
I don't want to complicate things too much, but I feel I ought to say there is a chance it is not a septarian nodule; it could be a volcanic bomb. They have a range of shapes, including ones with a cracked surface ('breadcrust bombs') somehwat like yours. I can't find any really good photos, but this one gives a rough idea.
If it is volcanic, it would be of similar age (possibly from the Troon Volcanic Member).
To decide between septarian nodule (in sedimentary rock) and volcanic bomb, photographs would probably not be adequate. One would need to:
- look at a thin section of the specimen, using a microscope (that would show the minerals and textures)
- saw the specimen in half, to see its internal structure
Thanks for the information Mike It is brilliant to be able to pick the minds of experts. I shall explain to Leon as best as I can.
Would it be of interest to my local NHM? If so I will gladly hand it in.
I can't say if your local NHM would be interested or not.
But I am sure it is worth taking it along to find out, because:
- they might be delighted
- they may have other similar ones that have been definitely IDd (so you would know for sure)
- you might find other things of interest to you / Leon
- you might make a useful contact for future use