Sandstone, mudstone, or just dried soil?

[gen]

Hi everyone!

 

I was playing around with some matrix fragments from the phosphate deposits of Morocco and decided to give it a dip in water to see what would happen.

 

What surprised me is how quickly the pieces crumbled into tiny clumps. Practically 80% of the matrix was gone in less than 10 seconds, dissolved by the water. I could very well have picked up a piece from dried mud and it would give similar results.

 

I always thought the Moroccan stuff was a kind of sandstone, but what I saw suggests it is more of a clay-type rock?

 

Then again, can the matrix even be considered a rock given how "fragile" it is?

 

Would love to hear your thoughts!

 

Jay

 

 

[ynot]

Many "sandstone" matrices are poorly consolidated and will separate when wet or with a little pressure.

It could even be clays that are holding it together.

[JohnBrewer]

Hi Jay

 

there are many fakes from Morocco, more than genuine fossils. Often they do include something real but then are enhanced. One example is mosasaur teeth. The tooth is reconstructed to include the root. The root part is often made from plaster and modern animal bone. Submerging in water will leave a cheap tooth rather than a more desirable tooth with root. 

[gen]

Thanks for the replies. There were practically no sand sized grains in there, only bits of bone and tiny shark teeth. So I was thinking maybe the practice of calling it "sandstone" isn't very accurate. Perhaps mudstone may be a better description? 

 

I get that the matrix feels somewhat sandy when handled, but these "sand" grains are really tiny. It may be fine sand perhaps, but most of the matrix still seems to be water-soluble clay.

 

John, that was also something I noticed. Everything disappeared except some clumps and tooth fragments. The matrix was really soft when wet. I lost part of a fish vert too before I took it out of the water. That may be why we see a disproportionate amount of teeth coming from Morocco - the bones don't survive wetting.

 

Jay

 

 

[JohnBrewer]

I think real fossil bones are fine but often repaired. The very fine sandy stuff I've come across such as used to fabricate the mosasaur jaws is water soluble.  

 

I have a limited knowledge of Moroccan fossils but @LordTrilobite has extensive knowledge and experience with fossils from this area. 

[LordTrilobite]

Yeah so speaking just about the actual real fossils from the Khouribga area in Morocco. The pieces of matrix can vary wildly in terms of structure. On some pieces of matrix you can use you hands to brush off grains of sand and will completely dissolve in water when you submerge them. This will also make some bones very fragile though. Some pieces of matrix get softer but still retain their shape when submerged. And some fossils are embedded in very hard stone that is not easily dissolved as far as I know.

 

If a piece of matrix mostly or completely dissolves, especially the fish bones seem to get very fragile from submerging. Sometimes having part of a bone exposed first and consolidating just the bone might help stabilise it when trying to dissolve the matrix surrounding it. Another maybe better way to use water on Khouribga fossils is applying water to a small brush so you can get parts of the matrix wet and soft so it's easier to prep. That way you won't get a mess of loose sand and fragile bones.

 

 

 

But I'm definitely not an expert either. I haven't used water on Khouribga fossils a whole lot to prep them, just occasionally. But yeah, different specimens may yield different results.