Variability of igneous rocks and its significance

Abstract

The types of specimens and chemical data used and needed for establishing the nature, variability and genesis of igneous (particularly granitic) rocks are examined. Specialization (by professionals and amateurs) within subdisciplines and the explosion in acquisition and statistical analysis of petrological data have led to lack of the necessary integration between dissimilar approaches. Some significant topics stemming from mathematical geology that are relevant to petrology are reviewed briefly (e.g. genetic process-response models, relevant sample populations and sample-data variance, classification and partitioning, and various methods of avoiding inherent difficulties in use of percentage data). An example of using compositional data to test quantitatively a genetic hypothesis for a granitoid suite is given.