Answer:
There are two explanations to this: covalent network bonding and carbon-silicate cycle.
Explanation:
A network solid or covalent network solid is a chemical compound which is formed through a continued network of atoms or molecules held together by a covalent bond throughout the system. An example included C-C bond in graphite or C-Si bond in silicon carbide (tentative reaction equation below):
xSiO2 + yCO2→ SixCyO(2x+2y)
Si-Si bonds are not as strong as C-C bonds and can easily be displaced as the particles react with atmospheric CO2.
The second scenerio is when silicates such as calcium silicate CaSiO3, or wollastonite, reacts with atmospheric carbon dioxide and water to yield a calcium ion, Ca2+, a bicarbonate ion, HCO3-, and dissolved silica. This process occurs during carbon-silicate cycle and increase organic carbon content:
2CO2 + H2) + CaSiO3 → + SiO2CaCO3 + CO2 + H2)
