Animal or black rock inside light rock

[Okie]

Animal fossil or a black rock fully encased in a light colored rock? Photos are what I'll call top (with the chipped off piece), bottom and side. Found on the east end of the much eroded Arbuckle Mtns in south-central Oklahoma (Murray County), laying on the ground. The black rock within it is exposed in the chip of light rock purposely broken off by my brother. This piece fascinates me and I really hope someone here can identify what it is. My first guess was a squashed geode but the exterior doesn't look anything like the geodes with which I'm familiar. Fossilized animal poop? Just an unusual (or usual) naturally occurring rock?

.....If you aren't familiar with the variety of fossils and ages found in and around the much eroded Arbuckle Mtns. I'll elaborated with my very limited knowledge.

[Okie]

These photos don't appear very clear here. I can take more if you'd like.

[TqB]

That looks like a chert nodule with a weathered crust, showing a fresh surface with typical conchoidal fracture where the flake has been knocked off.

Edited November 13, 2015 by TqB

[Raggedy Man]

Agreed- chert nodule

[abyssunder]

I think that could be, also, a flint nodule, because as visible the internal part looks glassy/waxy black or dark grey with yellowish-brown in contrast with the immediate external thin layer which is more lighter in color and goes to a rough texture. I don't see biological material in the inside, although sometimes flint/chert nodules contain fossils.

[Okie]

Boy, do I feel dumb! I've been furiously googling and reading to familiarize myself with the terminology you've used and each article led me to other terms....and photos. I'm very grateful for your identification of this piece and just can't thank you enough for giving me a bit of education.

[howard_l]

Here is something I found that explanes the difference between them.

Chalcedony Chert and Flint

Chalcedony is a variety of cryptocrystalline quartz with extremely small crystals and a specific gravity (weight under water, a measure of a rock/mineral's purity) nearly identical to that of pure quartz. Due to its very high quartz content and super fine particle matrix, chalcedony has a very waxy luster.

Chert is composed of larger crystal particles and has a specific gravity similar that of pure quartz. Due to impurities and larger particle sizes, chert is somewhat less "quartz-like" than chalcedony. Chert is duller and more opaque than chalcedony and its luster ranges from non-existant to very waxy, depending on the individual rock formation.

So what is flint? By mineralogical definition, flint is simply black chert. It appears that the term "flint" was originally applied to the high quality black cherts found in England. Over the years names have evolved for local chert formations/deposits that may include the word "flint" and technically speaking these would be incorrect more often than not. The reality of the flint verses chert debate is that in most cases it is something like "splitting hairs", there really is very little difference, chemically speaking. Artifact collectors tend to call materials that have a more waxy luster "flints" and those which have less luster to no luster "cherts". The difference between them lyes in their purity relative to pure quartz and their matrix particle size. The smaller the particle size and the purer the material, the more likely we collectors would be to call the material flint. To a purist, we would be wrong. A generalist would say "close enough".

Note: Some examples of Flint Ridge Flint are known to be 98.93 % pure silicon dioxide.

[Okie]

Thank you for the information, Howard_I. I'm doing my best to absorb it all. Also, it has me inspired to go find more pieces. I'll try not to embarrass myself again by posting it here and asking if it's an animal fossil. Haha!

[howard_l]

Don't worry about that just have fun collecting, you can learn as you go.