I am really hoping these are not just rocks. I've spent a lot of time gathering these recently and my collection has grown rather large. Please give me some good news lol! The one in my hand in the last pic weighs 28 grams. They are all very heavy for their size>>
In general, the relaibility of coprolite ID depends on the presence of;
- fragments of what was once food - plant or animal, sometimes pelleted
- external shape - distinct turd characteristics
- association with the pooer in time and place
- chemical composition - perhaps phospatic
For any one specimen, the more of those boxes that can be ticked, the greater the reliability of the ID.
But many specimens are unclear on those points.
And some of the unclear ones can be very difficult to distinguish from other things. There is real overlap in the classifiction: in some cases, pyrite/marcasite nodules may represent coprolites, for instance.
With 'possible coprolites', one should try to ID them as other things. Some rusty-brown lumps turn out to be industrial waste; others fossil nuts. If you can't ID them as anything, they really be nothing of significance - just a lump of something.
In your case:
- I see no evidence of food remains, but I am going only on your photos
- the external shape could be more convincing
- I don't know about the time/place/association - were there fossil animals in the same rocks that might have been the poopetrators?
- some of them look like 'just' marcasite nodules
- I think coprolite is also possible for most of those; not the angular one.
I suggest you crack one open to see if it has the usual marcasite structure (fine crystals radiating from a more-plain core).
Be happy with marcasite nodules, assuming they are so.
Learn to accept that it is not possible to ID everything, at least not without deeper research - which may require equipment, skills and knowledge beyond one's current means.
By all means continue posting here - that's one way of accessing others' expertise and experience. It also gives responders, like me, a chance to see things we have never seen before.
I looked into marcasite and I'll be happy with that as well! Kinda got me excited lol. Really I may be a little disappointed if turn out to be "just rocks" or something, but I'll get over it . I live in Fort Worth, Tx and the ground here is littered with fossils! At least in the few places that have not yet been bulldozen over and built on. I got the nodules from a field by my place where I've been collecting fossils. I say fossil "collecting" instead of fossil "hunting" because they are everywhere and you don't have to look very hard at all. You can tell from the landscape that it was once a river. The nodules are all scattered about, half way buried, mixed with the fossils. I was only able to upload 6 photos and didn't realize that I'd only uploaded one side of each nodule. Some of them were broken when i found them so i have photos of the inside of them. Most of them are rather sparkly and crystalized on the inside but they are mostly just black and brown, with no real pattern. just splotchy.
A few more picsA couple of them have (what looks to me to be) fossils/ imprints of fossils on them. A few also have 2 tiny holes and what looks like some sort of insect burrow. Never 1 hole, always 2. you can see one one the nodule on the right side. i flipped it in the next pic so you can see the other hole.One the left is the opposite side of the one in pic above.The one on the right is the other side of the one in above pic.
Definitely marcasite nodules, and they may be coprolitic.
Why you have so many scattered around, I can't say. I can say lucky you, though!
Where I grew up, on the chalk of SE England, marcasite nodules occur in the chalk, but they are relatively rare.
Some of yours are cracked open, so the once sparkly crystal interiors have weathered to rust. But the radial structure and massive core are still visible. If you break a fragment open, it could still be sparkly inside (as you have discovered) - it depends how long they have been weathering (and marcasite is less stable than its relative, pyrite).
The holes you mention are where the cores have 'rotted' and fallen away.
Fossil imprints, or indeed fossils, are possible. However, in those cases, the nodule might be a different iron mineral, such as limonite or siderite. Have a read of this on ironstones - http://en.wikipedia.org/wiki/Ironstone.
I have not been online for a while (technical difficulties lol) but I wanted to make sure to tell you that your detailed response is so very appreciated, as always... I spent some time on google looking into marcasite and ironstone etc, there are just sooo many possibilities lol! I did get a little bummed out after researching marcasite but I got over it... Looks like it is very common for marcasite to disintegrate, especially after being exposed to oxygen. I noticed a slight odor coming from some of them especially after they got wet. I read marcasite can put off a sulfuric smell usually meaning the disintegration process has begun ! I put some of them in air tight ziplock freezer bags lol. We will just have to wait and see what happens... Anyway Mike, Thanks for the info! I have a few more fossils I'm having a hard time identifying so I am about to post another discussion or two... Check them out if you get a chance!
i used to collect these from chalk and beachy head has tons of them! incertainplaces! radiating structure are definitly pyrite or marcasite and beenexposed along time which accounts for the rust if they are not rusted through theywill shine likegold if freshlybroken however they will rust moreexposed to air esp if they are maracasite and change to limonite
i havea nodule that was fresh in 80´s The centre is nowlimonite witha selenite growing too
Did you ever get any better answers on this question? Your pictures were the first of any I've seen like my own collection. The closest thing I could find to the ones that ARE NOT shiney and cystalike inside was a picture of titanium ore and a picture of geothite and hematite. At first I thought they were iron ore, but I kept looking because they didn't stick to a magnet, which iron should. You find out anything new?