Major elements: usually greater than 1%



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Major elements: usually greater than 1%

  • Major elements: usually greater than 1%

    • SiO2 Al2O3 FeO* MgO CaO Na2O K2O H2O
  • Minor elements: usually 0.1 - 1%

    • TiO2 MnO P2O5 CO2
  • Trace elements: usually < 0.1%

    • everything else






Mode is the volume % of minerals seen

  • Mode is the volume % of minerals seen

  • Norm is a calculated “idealized” mineralogy









Example: AFM diagram

  • Example: AFM diagram

  • (alkalis-FeO*-MgO)







Harker diagram



Extrapolate BA  B and further to low SiO2

  • Extrapolate BA  B and further to low SiO2

  • K2O is first element to  0 (at SiO2 = 46.5)









Can chemistry be used to distinguish families of magma types?

  • Can chemistry be used to distinguish families of magma types?



Early on it was recognized that some chemical parameters were very useful in regard to distinguishing magmatic groups

  • Early on it was recognized that some chemical parameters were very useful in regard to distinguishing magmatic groups

    • Total Alkalis (Na2O + K2O)
    • Silica (SiO2) and silica saturation
    • Alumina (Al2O3)





























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