Abstract
The composition of the average igneous rock has been calculated utilizing new analytical data and paying special attention to the role of andesites. The resulting composition, waterfree and in weight per cent, is: SiO 2 62.6; TiO 2 0.75; Al 2O 3 15.7; Fe 2O 3 2.85; FeO 3.29; MnO 0.14; MgO 2.87; CaO 4.80; Na 2O 3.30; K 2O 3.23 and P 2O 5 0.27. This is very close to earlier estimates based on geochemical balance equations. The calculated ratio of limestone to other sedimentary rocks differs markedly from current estimates. It is suggested that this discrepancy arises from the fact that metamorphic terrains are left out of consideration in such estimates.
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