Chert coloring

[Vnaz50]

On this piece of chert it appears to have either an iron or copper coloring at the top but a green undertone at the bottom. 
On the second picture I’m assuming that was caused by erosion. 
What would create the green undertone coloring? 

[JohnJ]

It doesn't have the typical characteristics of chert.  The green could be microscopic algae.

[erose]

I suspect this is Dolomite.