Pyritic Nodule (Whitby Cannonball) information

Pyritic concretions (know to locals as “cannon balls”) can also be found throughout the shales in the Jet rock. However Pyritic concretions occur in many shapes and sizes in the different Beds. For example in Bed 19 the nodules are larger then normal with the largest I have observed being two and a half feet long by one and a half feet wide! It is in Bed 22 where we tend to find the almost perfectly round nodules and as such this Bed is known locally as the “cannon ball Bed”.

A Pyritic nodule cracked open to reveal a Ammonite inside

A Pyritic nodule cracked open to reveal a Ammonite inside

These pyritic nodules are generally made up of a pyrite skin (around half an inch thick) surrounding a limestone core. It is inside the limestone core that Ammonites are commonly found, usually these specimens are in a great state of preservation most being almost uncrushed by the vast pressures generated in the fossilisation process. This can be clearly seen in the picture attached the ammonite shown is the gorgeous Eleganticeras and a common find within these nodules.
Not all “cannon balls” will have Ammonites in them so it is advisable to crack them open (wear the appropriate safety clothing….) before lugging them back with you, they can get quite heavy after a while……!
The “cannon balls” are washed out of the Jet rock by the tide action and can readily be found all along the North Yorkshire coastline stretching from Robin Hoods Bay to Runswick. If you are lucky enough to find one, protect it from Pyrite disease by keeping it contained with a small bag of silica gel.

It is possible to prepare the pyritic crust to form a smooth polished finish on some ‘cannonballs’. The result is stunning, however the methods are dangerous due to the nature of Iron Pyrite. Iron Pyrite has been used as an effective fire-starting stone for centuries. When struck, Pyritic nodules give off sparks, these sparks are small pieces of Iron Pyrite that have broken off and instantly react with the oxygen in the air. It is therefore easy to see how grinding, cutting, polishing or breaking pyritic nodules can be a hazard. Take care out there people!

To identify a pyritic nodule is an easy task. Firstly, it will have a strange texture compared with other nodules, even if sea-washed these nodules are generally rough to touch. The second property you will notice is the density, they are much heavier than most other objects of the same size found on the beach, it will feel like you are holding a solid lump of metal. Upon striking the nodule with a rock hammer, you may notice sparks being emitted and also a strong smell of sulphur burning (rotten egg smell) The last clue will be within the nodule once opened. You will see a ring of gold pyrite around the outside edge of the nodule.

A polished Pyritic Nodule

A polished Pyritic Nodule


2 thoughts on “Pyritic Nodule (Whitby Cannonball) information

  1. Hi mintsauce96.
    While fossilling near Whitby a couple of weeks ago, I came across the fossil of a shell which I can only describe as being similar to a clam in appearance and about 100mm/4″ across.
    It seems that the top surface of the shell is coated in an extremely thin Pyritic ‘leaf’. This surprises me as I did not know that Pyrite could form in this way, especially as there does not appear to be any cracking in the ‘leaf’.
    This is really puzzling me, and I am struggling to find an answer. Could you possibly confirm if it is likely to be a thin Pyritic coating, or if it could be anything else?

    I have photos, but the know-how of how to upload them to this post.

  2. Hi Chris,

    Great to hear you have been out beach combing and have found something to take home.

    The golden sheen you have is indeed, pyrite. It is common for fossils from this area to become pyritised due to the bacteriological conversion of organic matter into sulphides. Be careful as pyrite in certain forms can degrade with exposure to moisture and particularly saline water. The thin layer you have is usually reasonably stable but you may want to keep an eye on it and protect it if you notice any degradation.

    Happy hunting 😉 Kev.

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