On the chemical identification and classification of minerals
To univocally identify mineral species on the basis of their formula, the IMA-CNMNC recommends the use of the dominant-valency rule and/or the site-total-charge approach, which can be considered two procedures complementary to each other for mineral identification. In this regard, several worked examples are provided in this study along with some simple suggestions for a more consistent terminology and a straightforward use of mineral formulae. IMA-CNMNC guidelines subordinate the mineral structure to the mineral chemistry in the hierarchical scheme adopted for classification. Indeed, a contradiction appears when we first classify mineral species to form classes (based on their chemistry) and subsequently we group together them to form supergroups (based on their structure topology): To date, more than half of recognized mineral supergroups include species with different anions or anionic complexes. This observation is in contrast to the current use of chemical composition as the distinguishing factor at the highest level of mineral classification.