Primary minerals are the minerals that crystalize during the formation of Earths crust, and their typical δSi isotopic value is in the range of −0.9‰ – +1.4‰. Earths crust is constantly undergoing weathering processes, which dissolve Si and produce secondary Si minerals simultaneously. The formation of secondary Si discriminates against the heavy Si isotope (Si), creating minerals with relatively low δSi isotopic values (−3‰ – +2.5‰, mean: −1.1‰). It has been suggested that this isotopic fractionation is controlled by the kinetic isotope effect of Si adsorption to Aluminum hydroxides, which takes place in early stages of weathering. As a result of incorporation of lighter Si isotopes into secondary minerals, the remaining dissolved Si will be relative enriched in the heavy Si isotope (Si), and associated with relatively high δSi isotopic values (−1‰ – +2‰, mean: +0.8‰). The dissolved Si is often transported by rivers to the oceans.