12 April 2017
Check this out:
That’s a beautiful example of weathering in a dolerite dike on Arran. The igneous rock was broken along two more or less perpendicular joint sets, and then fluid flow along those fractures helped “rot” the adjacent rock through oxidation and hydrolysis. The resulting brownish weathering rind grows at the expense of the unweathered black rock. Because there is more surface area at the corners of the rock blocks (where two joints intersect), there is more weathering there, and thus the blocks of rock become increasingly spheroidal over time.