Minerals and rocks on earth frequently have contact with water in the form of moisture (air) or liquid. A systematic conversion of the component in mineral lead to formation of water bonded composition compounds. Water flow all over the land and underground in the form of rivers and due to rain the surface of the earth get wet. Water from wet land penetrates to some extent down the earth surface. Water makes a contact with the mineral available at that surface. Changes in mineral take place by physical and chemical means due to dissolution and hydration. Dissolution of mineral happen as water enhances the component to disperse in it by physical phenomena. Hydration occur when water molecule react with the element in minerals. Minerals like anhydrite calcium sulphate and olivine (Mg2SiO4) are exposed to water they hydrate.
Explained by the reaction,
CaSO4 + 2H2O →CaSO4.2H2O Gypsum is formed. The component adds up water molecules that increase its volume by 33%.
Mg2SiO4 + xH2O→ Mg2SiO4.xH2O this reaction show how serpentine is formed when olivine is reacted with water on contact. These reactions occur at ambient conditions.
A familiar rock mineral, sodium chloride (rock salt) and gypsum admit the dissolution action with water. Bicarbonates of metal are easily soluble than carbonates. Carbon dioxide when reacted with calcium, magnesium and iron in presence of water converts to calcium bicarbonate, magnesium bicarbonate. Water attains temporary hardness due to this soluble form of bicarbonates of metals.
CaCO3 + CO2 + H2O → Ca(HCO3)2
MgCO3 + CO2+ H2O → Mg(HCO3)2
Water contains some dissolved carbon dioxide and the water with CO2 in it coverts sodium, potassium into soluble form as above. Rocks of potassium with silicate and alumina changes as the reaction
K2OAl2O3.6SiO2 + CO2 + H2O → Al2O3. 2SiO2 + K2CO3 + 4SiO2