Over time, the net effect of weathering is to break rocks into smaller and smaller pieces, which results in an exponential increase in the surface area. Minerals in the rock, often the Fe-rich ones, react with oxygen to form new minerals. Think back to Bowen s reaction series. Weathering conditions on the surface are closest to the conditions of formation of quartz and other silica-rich minerals, so those minerals are most stable under surface conditions. Generally, where there is more liquid water, more weathering occurs.
Mountain tops have frequent freeze and thaw cycles, where as the valleys have fewer.
Therefore, rocks on the mountaintops will be subjected to more weathering. The end product of mechanical and chemical weathering is regolith , which is the term for weathered rock. Regolith is the principal component of soil.