Another thing I saw last Friday on my DC field trip was this fine boulder exhibiting spheroidal weathering:
Annotated:
It’s a boulder of the Laurel Formation, a clast-poor metamorphic unit found east of the Rock Creek Shear Zone in DC.
This is the first time I’ve seen it exhibit this sort of mechanical weathering. Compare it to this example from Montana or this example from the Causeway basalts of Northern Ireland.
I wonder if it’s a result of fire spalling? cool find.
see a few examples on: http://www.gomeraflora.de/Vulkanbomben%20etc.htm