Looking for identification - Rock in North West Territories - CA

[geo.baker]

Big fascinating rock on the Mackenzie River bank. The only one like this found so far around the place. 

Silicified mudstone? what is the white part ?

 

Thank you for your suggestion. 

 

 

[phoscorite]

Hello

 

It seems that you got a highly deformed sample.

The white bands look like boudinaged (folded) silica layers in a more ductile black matrix.

Whithout any posibility to check the trace, density or magnetic susceptibility of your sample, it is difficult to answer more seriously.

But your specimen could be a piece o folded BIF (banded iron formation).

Alternatively, the white bands could represent biogenic silica (silexite, chert) in a black carbonate matrix, hence a HCl testing is required.

[jean francois06]

Tests are missing.  Are you sure it's silicified? Grains in light levels look coarser. Bioturbation? 

It seems that these clear levels have some sort of cortex ( chert hypothesis), or it is chemical, with iron transfer.

[phoscorite]

il y a 18 minutes, jean francois06 a dit :

Are you sure it's silicified?

Just silica in my opinion. The main (visual) argument is that the folding pattern indicates that the white layers are definitively more competent than the black host, so the silica hypothesis is the simplest one.

il y a 22 minutes, jean francois06 a dit :

these clear levels have some sort of cortex

Correct, looks like a silexite. Its almost impossible to discuss if this represents a reaction halo between the two components without any chemical information about them.

[jean francois06]

il y a 4 minutes, phoscorite a dit :

Just silica in my opinion. The main (visual) argument is that the folding pattern indicates that the white layers are definitively more competent than the black host, so the silica hypothesis is the simplest one.

 

Je pense aussi, mais des carbonates altérés dans un contexte de rivière  peuvent prendre cet aspect. Quant aux plis, c'est pas évident. Comment les construire à partir de cette photo par exemple, qui donne une vue 3D :

I think so too, but altered carbonate pebbles in a river can take this aspect. As for the folds, it's not obvious. How to build them from this photo  which gives a 3D view ?: