Posted: Nov 04, 2018 5:01 pm
by Cito di Pense
Adco wrote:In the 3rd picture, the one with the hollows: were the hollows formed through water erosion? I can see clearly that those hollows only formed below the old water line, i.e. where soil retained water. There are no hollows above ground. Also, at depths greater than where the water would sit, there are no hollows and it looks the same as the rock above the ground line. That tells me that water sitting in soil against the rock face would react with the white chips and erode them through some chemical process.

It's painful to see you keep puzzling about this three years on with nothing better to show than a few crude photographs. You haven't been able to identify whether this is an igneous, sedimentary, or metamorphic texture. You haven't reassured me that the white inclusions are quartz. although the fracturing is suggestive. For all we know, this could be a metamorphosed sedimentary rock that had irregularly-shaped quartz pebbles in it. You can't even show which way is "up" in the rock as it was originally deposited. If it is a metamorphic texture, good luck with finding "up" if all you have is that. You don't know which way was up when the differential weathering was taking place that removed some of the inclusions. There are no questions about this rock that you've been able to answer definitively. How dense is the matrix, which you say is 'blue". If it's quite dense, odds-on this is a metamorphic rock. It's possible that the clasts or pebbles that are missing did not dissolve, but were simply washed away when the matrix around them weathered. See what I mean?

If the pebbles are quartz, it's unlikely they dissoved. Quartz is pretty resistant to weathering in a water-saturated environment, but it's not even clear from the photos that these are crystals of quartz and not chunks of polycrystalline quartz or some other light-colored mineral.