Proposed Change in Calculation of Norms of Rocks.

Abstract.

It is proposed that the following normative pyroxene minerals be used: CaSiO₃, MgSiO₃, and FeSiO₃ (with symbols “wo,” “en,” and “ hy,” respectively); and that the olivine molecule be given in terms of Mg₂SiO₄ and Fe₂SiO₄ (with symbols “ fo ” and “fa”). It is shown that these changes will improve the norm by bringing the ferro-magnesian minerals into a closer approach to natural conditions, by making it easier to survey their composition, and by rendering calculations simpler.