Geology 37, 615–618 (2009)

How does a rock weather away into clay? Usually, it is helped along by fungi, in a process now examined in detail by Steeve Bonneville at the University of Leeds, UK, and his colleagues.

The team grew tree seedlings and a symbiotic fungus Paxillus involutus in an experimental set-up that included the mineral biotite, and followed the action with high-resolution microscopy. The fungus enhances the weathering of biotite, not by exuding chemically active substances as was previously thought, but by physically disrupting the structure of the mineral with its hyphae. This is followed by chemical changes as the fungus removes potassium and oxidizes iron within the mineral. Soon, the rock is no more.