A surprise find on Seacliff beach

Septarian nodule (2)
Mystery object – Septarian nodule from Ingleton

A while ago on The Hazel Tree – almost a year ago to the day, in fact – I posted a fun quiz, asking you to identify a mystery object.

This was a septarian nodule, a strange-looking geological formation created millions of years ago when clay or mud settled around a nucleus – which could be the shell of a crustacean.   This lump later dried out and cracked when it was exposed to the air.   Later still, some kind of mineral-bearing liquid seeped into the cracks, lining them with crystals, which you might see if you broke it open.

I bought this septarian nodule at a rock shop in Ingleton, West Yorkshire (sadly, the shop has since closed).

Little did I imagine, wandering around the beach below Tantallon Castle a couple of weeks ago, that I might pick up another.

Seacliff beach, Tantallon, East Lothian

Tantallon rock

There it is… half-submerged in wet sand.   I could hardly believe my eyes, although I didn’t at first know what it was.

But when I posted a photo on Twitter with a request for help in identifying it, members of the Geological Society of London told me they suspected it was either a septarian nodule or a septarian concretion (and to geologists there is a fine distinction between the two).

They suggested that the base rock was some kind of mudstone, and that a mineral such as quartz was filling the cracks.  Apparently, these are quite common in East Lothian.

So, here it is… my new precious!

Septarian nodule

Tantallon (1)Tantallon Castle is worth a visit in any weather (unless it’s blowing a gale!)  Click on the photo to find out more.

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  • justbod

    They’re beautiful! Our countryside holds so much beauty, and surprises.
    I do remember seeing a very small one once (most like your bottom picture), I think it was in a North Yorkshire stream….but that was many years ago, so I may be mistaken. I was with something who was ‘hunting’ for them and he told me how rare they are. I always thought they looked a little like a strange fossilised tortoise!
    Glad you found out what it is!

    • Jo Woolf

      Yes! The guy in the Ingleton shop said they were found in the streams locally. And when I lived in North Wales, an old farmer brought me one to look at – one of his friends had found it in a stream, and he didn’t know what it was. He thought I would know the answer, but at the time I didn’t. That’s exactly what I thought it looked like, a fossilised tortoise! 🙂

  • blosslyn

    I like the photo of it in the water, it looks like some sea creature laying in wait for lunch to crawl pass, but what is a mud stone and where does the quartz come from and did this happen in the water or on land and is like the other stone, did it happen million of years ago……sorry just quite fascinated by it and I know nothing about rocks or stones. Although I collect them on the beaches in Wales, because I like the shapes and colours…..but you have now got me interested in what they are 🙂

    • Jo Woolf

      I know, isn’t it amazing?! Aha, some geology is required! I will do my best!
      A long, long time ago……..! Septarian concretions are believed to have formed underwater, in the Cretaceous period, which was between 50 to 70 million years ago. The dead bodies of small sea creatures sank to the bottom where they started decomposing. As they did this, layers of mud and silt collected around them, forming small ‘balls’ on the ocean floor.
      Much later, when the oceans receded, the balls of mud were left to dry out, and in doing so they cracked. Under intense heat and pressure from volcanic activity, the mud balls were turned to stone but still with the cracks in them (a bit like clay in a kiln, I guess).
      Millions of years later (probably!), some kind of mineral-bearing liquid was forced up through the Earth, again from volcanic activity, and seeped into the cracks, slowly forming crystals.
      So most septarian concretions have a fossil at their core. The word ‘septarian’ comes from ‘sept’, meaning ‘seven’, and many examples have seven radiating cracks, for reasons geologists don’t understand. Mine doesn’t – it looks more like a road map – but I would say that the rock itself does look as if it has been clay at some point.
      I hope that this makes sense! I won’t be asking questions! 🙂
      You can read more here, too:

      • blosslyn

        Thats amazing, so it could have been a creature to begin with, even if it was really tiny…..just think what that ‘rock’ has been throught, how old it is……..just amazing, thank you for the natural history lesson, I shall be keep more of a look out from now on 🙂

  • David Litchfield

    I used to live in Anstruther in Scotland and you’d find these very commonly if you walked along the coast to Crail. I used to have about 20 or so displayed on a shelf. I since moved away from the UK and left them behind 🙁 Anyway, I never knew what they were called until reading your article so thank you!

    • Jo Woolf

      Oh no! But wonderful to have found 20 of them! I guess you know where to look if you ever come back! I had no idea they could be found in such quantities. You are very welcome – really glad you enjoyed the article!

  • Derek Marlborough

    ‘Septarian nodule or a septarian concretion’!
    Thanks for filling this gap in my pitifully small knowledge of geology Jo.
    I regularly see these on the foreshore south of Carsethorn on the Nith Estuary, south of Dumfries and have often puzzled over their creation. I find them particularly attractive when they’re wet – dark red ‘pebbles’, shot through with almost pure white fissures.
    Carsethorn was the ‘Fever Port’ for Dumfries. Ships returning from abroad were quarantined at Carsethorn to reduce the risk of yellow fever etc being brought home from the colonies in the 18-19th centuries. Carsethorn was also a feeder port, connecting Dumfries with Workington, Liverpool and the wider world, by steam packet. As a consequence of this previous activity I often find very old, worn glass bottle and assorted china fragments – which is my interest in the area.
    More info here:
    After a stroll along the beach, The Steamboat Inn will do you a very nice lunch in the cosy bar.

    • Jo Woolf

      Hi Derek, really happy to have helped to solve that for you! Wonderful that you’re finding them down on the Dumfries coast. We were told of a place in Yorkshire where you can find them in a river, but we didn’t have time to walk there to investigate. Very interested to hear about the history of Carsethorn, and your findings of glass and china fragments. Love beachcombing at the best of times! It’s nice when there’s a particular history attached to it. Thanks so much and if we’re ever in the area we’ll check out the Steamboat! Best wishes, Jo

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