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Leithl
6FC5387F-9F8B-4E18-BB75-F60283FDD9F7.jpeg  311AAD8E-63B0-4888-9D1D-027400294780.jpeg  5E2FA66A-09B7-4D7C-B857-AFFFDAA370BA.jpeg  My mother found this today on an outcrop of Jurassic age rocks on the West of Scotland. It has the same markings on both sides, has slight magnetism and a sulphorous smell. Any ideas if this could be a fossil?
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prep01
Hello and welcome to the forum. I believe that this is scoured rock with a very high Iron Pyrites / Iron content I'm afraid.
Colin Huller
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Barrow Museum
There are many outcrops of Jurassic rocks in Western Scotland, from a tiny patch in the Arran volcanic vent, through Mull, Morvern, Ardnamurchan, the Small Isles, Skye, Applecross to again, a tiny patch, in Gruinard Bay.

However, what you are showing us is neither Jurassic nor a fossil.  It is a piece of igneous rock; a fine grained basalt, which originated from the Tertiary Volcanoes that intruded the Hebridean area about 60 million years ago and continued for up to 5 million years more.  Apart from actual volcanoes, a lot of this activity involved the injection under high pressure of sheets of molten basalt up cracks and faults in the country rock (including the Jurassic sediments). They form swarms of dykes (more or less vertical, cross cutting the strata) and sills (injected along bedding planes more or less horizontally). When this hot basalt encountered cool country rock, the margin chilled rapidly into an even finer, black, almost glassy texture.  What I see in your photo is a chunk of one of these sheets, maybe 10cm thick.  The rapid cooling has created a mini fracture pattern on the sides of the sheet, which has been enhanced by weathering after the rock fragment was eroded out of its original location.  The slight magnetism will be from the mineral Magnetite, which is a common component of these igneous rocks.

In the first photo.can I detect a chilled margin on the upper and lower surfaces and a sort of zoned appearance, looking a little coarser crystalline along the central plane?  It looks like it to me.  This is the effect of more rapid cooling along the edges.

I hope this helps explain what was found.
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Anonymous
Wow! Thanks everyone this is all so interesting! Ive just finished my first year of geology at Aberdeen so very keen to learn! Really appreciate your comments, fascinating!
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prep01
Hi BM, thanks for correcting me - I'm not conversant with that type of rock (especially just a photo)! It does look as though it's well travelled in a glacier though!
Colin Huller
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