Calculation of the CIPW norm: New formulas

[摘要] A completely new set of formulas,based on matrix algebra,has been suggested for the calculation of the CIPW norm for igneous rocks to achieve highly consistent and accurate norms.The suggested sequence of derivation of the normative minerals greatly deviates from the sequence followed in the classical scheme.The formulas are presented in a form convenient for error-free implementation in computer programs.Accurate formulas along with the use of variable molecular weights for CaO and FeO;corrected formula weights for apatite,pyrite and fluorite;and suggested measures to avoid significant rounding off errors to achieve absolute match between the sum of the input weights of the oxides and the sum of the weights of the estimated normative minerals.Using an analogous procedure for determining the oxidation ratios of igneous rocks as used in the SINCLAS system of Ver ma et al (2002,2003),the suggested calculation scheme exactly reproduces their results except for apatite for reasons explained in the text,but with a superior match between the totals for about 11,200 analyses representing rocks of a wide range of composition.

[学科分类] 天文学(综合)

[关键词] CIPW norm;igneous rock classification;oxidation ratio;standard igneous norm;normative minerals.