28 March 2017
Over the weekend, I saw this polished slab of countertop outside a hardware store in Berryville, Virginia. I stopped to check it out. What a beautiful conglomerate!
I noticed that many of the cobbles had pronounced weathering rinds:
Here’s another example:
Note the weird shapes of the grains around it – these embayed and flush grain boundaries are intriguing (yellow highlights):
These grain boundaries are indications that pressure solution has taken place in this rock.
They suggest this conglomerate was squeezed a bit, triggering pressure solution of certain minerals. Rocks rich in those minerals (probably quartz in this case) deformed with their most-highly-pressurized portions dissolving away (changing the shape of the cobble) as less soluble rocks pushed into them.
Explore the whole thing here:
Link 0.85 Gpx handheld GigaPan by Callan Bentley