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A question about the brachiopods Paraspirifer bownockeri

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Hello everyone,

I have been wondering about this for a bit but only now that I atually have one of these in my collections have I decided to ask this,

All of the P. bownockeri I have seen have been pyritized and I wanted to ask why this is, I do not know of any other brachiopods like this because while there are some I have seen preserved in pyrite they are from areas where the rest of the fossils are also pyritized, from what I have seen its mostly just this species that is commonly found fully pyritized from this formation.

The only thing I can think of is maybe they are found in a specific layer which is why they are the ones that are primarily pyritized.

So my question is, what causes this? Also do these brachiopods come preserved in other mineral such as calcite?

If anyone knows or has any useful sources I would love to hear it!

Thank you very much,



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In the book Strata and Megafossils of the Middle Devonian Silica Shale (Kesling & Chilman, 1985), P. bownockeri is described as follows: "The largest and (some would claim) the handsomest of Silica brachiopods, Paraspirifer bownockeri is a prize much sought after by the amateur collectors." It is listed as occurring in units 8, 9, and 11 (per the book's Silica Shale stratigraphic section), and unit 8 is described as having "all fossils strongly pyritized." From this, I would infer that you only see the pyritized Paraspirifer for sale because that's what collectors were hunting most, and because collectors would pay more for larger brachiopods as opposed to say smaller Mucrospirifer.


In my own experience, while I have not hunted the Sylvania quarry where I believe all the Paraspirifer came from, I have hunted at another locality where "pyritization" was extremely common. The vast majority of brachiopods, and even some other fauna, were "pyritized." (I put pyritized in quotes because it may have been replacement by another iron-based mineral. The specimens did not have the prized gold-coloration unfortunately)

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Tidgy's Dad

I have a few pyritized brachiopods from the Silica Shale, mostly Paraspirifer bownockeri, but I think I have one or two others. I will have to go and have a look at them. 

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