We investigated the mineral content and geochemical composition of the upper 6 m of regolith, formed by weathering of granitic rocks in Mediterranean and humid climate zones. We found that the development of the upper regolith in the Mediterranean climate is controlled by secondary minerals which cause fracturing and thus facilitate fluid infiltration to depth. The upper regolith in the humid climate is controlled by secondary minerals that cause a reduction of fluid infiltration to depth.

We measured the surface area of minerals in two 21 m cores from soil to bedrock to test hypotheses on the formation of the surface area of weathered rock. A sharp increase in high-surface-area secondary minerals extended from 3 m to the ground surface. Half the total surface area was from corroded iron minerals, which form in the presence of oxygen, even though corroded iron comprised less than 0.1 % of the rock. Element removal by rock dissolution started at 7 m but did not form new minerals.

Erosion modulates Earth's carbon cycle by exposing a variety of lithologies to chemical weathering. We measured water chemistry in streams on the eastern Tibetan Plateau that drain either metasedimentary or granitoid rocks. With increasing erosion, weathering shifts from being a CO₂ sink to being a CO₂ source for both lithologies. However, metasedimentary rocks typically weather 2–10 times faster than granitoids, with implications for the role of lithology in modulating the carbon cycle.