I found this unusually heavy rock at Charmouth. It has a base that looks like wood, and there is what looks like a small ammonite poking out of it. It feels and looks as if it might have iron in it, and is about 4cm long. What is it, please?
A very good find! well done.
Your specimen contains a high percentage of Iron Pyrites (fools gold) and by the look of your first two images could be related to Jurassic wood (200myo)
Will the moderator/administrator of this forum please forgive me in directing Minmi to having a look at 'that auction site in the sky' if you know what I meen because there are many specimens from the same area and this will help you to find more!
Also there is the local geological society for more information.
Good answer tabfish.
As tabfish said it definietly contains pyrite, but I don't think it contains wood, although pic4 looks like coral or maybe brachiopods/bivalves. Pic3 looks like it may be an ammonite, but the picture isn't clear enough to be sure. It also could be a bivalve/brachiopod, but I'm not sure. Could you send some more images from different angles so I can make a more accurate ID?
Oh dear, I fear you may have set us on different mental paths!
If we appear to be giving you conflicting answers, it is because:
- we come from different backgrounds
- your photos leave us guessing somewhat.
Anyway, this is how I see it...
Photo 1 & 2.
While I can't rule out a fossil explanation, my initial reaction is mineral. The cross section suggests 'vein', composed partly of a white mineral and a yellow-green mineral (perhaps epidote).
I think the wood-like part is just some of that latter mineral, which happens to have a somewhat regular pattern; but alternatively, it could be some of the host rock (to one side of the vein), partly impregnated with the yellow-green mineral.
(See 'epidote' on this page, for an example showing its colour.)
You state that it is heavy. If you mean unusually dense (ie. heavy for its size), that makes me suspect the white mineral could be baryte (the more common minerals would be calcite/quartz).
Photos 3 & 4.
I suspect these are echinoid fragments. The surface of many types of echinoid is composed of all sorts of lumps and bumps.
The rounded protuberances could be mamelons of tubercles (where spines attach and articulate).
The 'mini-ammonite' could be a jaw (I can't find a good match to yours, but search on this page to get a general idea of an echinoid's beak-like jaws); but it could be something else.
Those are my best guesses, going on the photos.
If you can, as Dan asks, post some sharper photos from different angles, that could help reduce the guesswork. But to be sure, a close-up inspection with hand lens and/or microscope would be necessary.
Thanks for the photos. There is definietly an ammonite in there, but I'm not sure what the spotty part is, I would think coral or maybe Echinoid fragments as Mike suggested.
Thanks for the further photos: godo job; helps a lot.
...And leads me to change my mind about the echinoid fragments...
Now I can see the lumps run smoothly into each other. That and other aspects lead me to think encrusting bryozoan is more likely, possibly a trepostome type. Note that the Trepostomata became extinct in the Triassic, and Dorset has Triassic rocks.
I suspect in your specimen, the bryozoan is encrusting other fossil fragments, such as the tiny lump that hints at ammonite.
Here are a couple of specimens with some similarities to yours
And, also similar, here is a bryozoan encrusting a brachiopod
General info on bryozoans:
1 - this is how some pyrite specimens are preserved from the area you found yours.
The trouble is yours looks so different because it has not been highly polished to give the surface a golden sheen.