Chemical Weathering and Chemical Sedimentary Minerals 
Cochise College   
Virtual Geology Museum             

Geology Home Page

Roger Weller, geology instructor
wellerr@cochise.edu
copyright 2007-R.Weller

     The primary igneous minerals, those found in Bowen's reaction series, are susceptible
to chemical weathering.  Water (H₂O), carbon dioxide (CO₂), and volcanic gases such as
sulfur dioxide (SO₂), hydrogen sulfide (H₂S), sulfuric acid (H₂SO₄), chlorine (Cl₂), hydrochloric
acid (HCl), and others are the prime chemicals responsible for the chemical weathering
processes which release cations.  The secondary or sedimentary minerals that form can be
changed into sedimentary rocks by evaporation and deposition.

primary                cations                         secondary                       chemical
igneous                released by                 sedimentary                   sedimentary
minerals               weathering                 minerals                         rocks

olivine                     Mg⁺²                 CaCO₃-calcite      ------------------limestone 
pyroxene                 Fe⁺²                 (Ca,Mg)CO₃-dolomite  -----------dolomite (dolostone)        
amphibole               Ca⁺²                 CaSO₄.2H₂O-gypsum  -----------gypsum (gypstone)
biotite                      Na⁺¹                 NaCl-halite  ---------------------------salt
plagioclase              Al⁺³                  clay minerals  -----------------------shale
orthoclase                K⁺¹                   KCl-sylvite ----------------------------potash salt
quartz                      Si⁺⁴                  SiO₂-quartz ---------------------------chert, flint, jasper
muscovite                                        SiO₂.nH₂0-opal  ---------------------opalite, sinter
                                                        Fe₃O₄-magnetite  ------------------iron ore
                                                        Fe₂O₃-hematite  --------------------iron ore
                                                        Fe₂O₃.nH₂O-limonite  ------------iron ore