Granite weathering
Weathering factors
Water: it acts in two ways. First, through hydration (the addition of water to a compound without chemically altering it). In micas, for example, water can slip between the layers of the mineral, causing it to swell, which gradually separates the grains of the rock. Water also acts through hydrolysis (the decomposition of a substance under the action of water).
Plants that have taken root on the surface of the massif (the action of roots in the joints and the action of organic molecules resulting from the decomposition of these plants).
Joints, accelerators of weathering
Although granite is a hard and resistant rock, it lacks flexibility. During tectonic movements, granite fractures into a juxtaposition of blocks separated by checkerboard-like fractures.
These fractures, known as joints, facilitate weathering by allowing water to circulate and have a large contact surface, and by allowing roots to penetrate more easily.
Spheroidal weathering and ball mills
The intersections of the joints then become areas that are more susceptible to weathering, and the corners become rounded while the central part remains largely unaffected. This is known as spheroidal weathering.
The joints widen more and more, and a mosaic of individual blocks gradually forms, leading to the “granite ball” stage.
And in the end, it's chaos!
Spherical weathering eventually produces cyclopean blocks with rounded shapes. The blocks gradually separate from each other, and those exposed on the surface, having become unstable and unbalanced, eventually fall to the foot of the cliff.
Only blocks that are not fractured do not weather deeply, leaving behind a chaotic granite landscape.
The disintegration of the granite in situ, followed by leaching, forms part of the sand on the beach.