Normative mineral inventory

The normative mineral inventory represents an idealized mineralogical composition of a rock . It is determined on the basis of a chemical analysis according to a calculation rule (a norm ). The normative mineral inventory is thus an alternative representation of such an analysis. It is often given in mol percent (mol%), but also converted into volume percent (vol%) or weight percent (wt%) for various questions . In contrast to the modal mineral inventory , the normative mineral inventory is a hypothetical property of a rock and only in special cases corresponds to the ratio of the minerals actually occurring in it.

Especially for fine-grained or vitreous volcanic rocks , the mineral composition of which cannot or only insufficiently be determined with microscopic means due to the fine-grainedness , the normative mineral composition is an important parameter for classification based on the mineral composition, e.g. B. in qapf diagram ,. Furthermore, it allows a quick comparison of different degrees crystallized rocks and makes statements about the state of saturation of certain species in the observed chemical system (eg. As the SiO ₂ saturation). This can be necessary for further petrological interpretations.

Well-known and frequently used standardized calculation rules are the CIPW standard and the Barth-Niggli standard .