Chemical Erosion can sometimes be quite artistic

[Ludwigia]

Last week I visited a new site in the Wutach Valley that a friend had told me about, but after 4 hours of digging and prying and not much to show for it, I decided to call it a day there and spend the remaining few hours checking out a plowed field in the viscinity which usually gave up a few modest finds. But this time I was in luck. The farmer had laid a long furrow on the edge of the field which was exposing a fossiliferously fruitful bed with which I was quite familiar: the Bajocian Macrocephalen-Oolite with among other things lots of Macrocephalites ammonites ripe for the harvest. All I had to do was a bit of hacking and scratching at the surface to get the blocks out. And I wasn't doing any damage to his fields.

The only drawback about field finds is that the fossils are often quite weathered and eroded. The acids in the humus react with the ground water and the substances in the fossils, in this case mostly iron and calcite, and eat away at them. In this case it wasn't so bad, though. Quite to the contrary, some really nice sculptures were a result of its work. The chemical reactions over the years have etched out the lobes and septa of the ammonites, creating some really distinctive and colorful patterns. Here's a typical example of a Macrocephalites jacquoti ammonite in this condition.

 

 

If anyone else would like to show some results of the working of chemical erosion, then please feel free to do so.

 

 

[Kane]

That looks quite lovely, actually. A truly natural acid-etching.  

[Fossildude19]

Nature's art.  

[Ludwigia]

24 minutes ago, Kane said:

That looks quite lovely, actually. A truly natural acid-etching.  

 

12 minutes ago, Fossildude19 said:

Nature's art.  

No need for HCl

[Ruger9a]

That's a beautiful specimen!

[FranzBernhard]

Very nice, thanks for sharing!

 

11 hours ago, Ludwigia said:

If anyone else would like to show some results of the working of chemical erosion, then please feel free to do so.

 

Sure! Nearly everything in this thread is due to natural humid acid etching. Neither breaking, nor polishing nor artificial etching gives such nice contrast combined with minor sculpture:

Franz Bernhard

[Ludwigia]

7 hours ago, Ruger9a said:

That's a beautiful specimen!

 

17 minutes ago, FranzBernhard said:

Very nice, thanks for sharing!

 

 

Sure! Nearly everything in this thread is due to natural humid acid etching. Neither breaking, nor polishing nor artificial etching gives such nice contrast combined with minor sculpture:

Franz Bernhard

Thanks guys and thank you for the link, Franz. I'd missed out on that one.

 

[Ludwigia]

More of the same. This time another Macrocephalites with a piece of the keel broken off revealing the septal chambers and then a Choffatia sp.

 

 

 

 

[Ludwigia]

I mentioned recently elsewhere in the forum that I paid the field another visit. My last one this time, since the material ran out, or rather was so eroded that it wasn't worth moving down along the line any more. But here are just a couple more to show. First a Cadoceras quenstedti, relatively seldomly found in this zone and then another Macrocephalites jacquoti.

 

 

 

 

[FossilNerd]

@Ludwigia

Can you explain more on what causes the acidic conditions? Is it a common occurrence in the fields in your area? I’m curious if it could be happening in some of my local farmer fields, or in my vegetable garden. Maybe I’ll plant a row of fossil next year. Lol

 

 You mentioned is was due to the acids in the humus reacting with the ground water. Is the humus an additive put in the soil by the farmer, or is it a by-product of farming, or both? Humus is basically decomposed plant matter so I could see it going either way. Added as a soil conditioner, or simply coming from the left over plant material after harvesting. 

[Ludwigia]

12 minutes ago, FossilNerd said:

@Ludwigia

Can you explain more on what causes the acidic conditions? Is it a common occurrence in the fields in your area? I’m curious if it could be happening in some of my local farmer fields, or in my vegetable garden. Maybe I’ll plant a row of fossil next year. Lol

 

 You mentioned is was due to the acids in the humus reacting with the ground water. Is the humus an additive put in the soil by the farmer, or is it a by-product of farming, or both? Humus is basically decomposed plant matter so I could see it going either way. Added as a soil conditioner, or simply coming from the left over plant material after harvesting. 

I can't add much more to what I've already written. It depends on what plant material makes up the humus. In the case of farming, then there is also any manure, etc. which the farmer spreads added to it and also any mineral fertilizer which he may use is added to the naturally present minerals and elements (a lot of iron being the case here) in and under the surface.