MafikGehalte

MafikGehalte is a term used in geology to denote the share of mafic minerals in a rock, typically expressed as a percentage of the rock's mineral content by weight or volume. The term combines the English "mafic" (from magnesium and iron-rich minerals) with the German word "Gehalte" meaning content. In practice, MafikGehalte provides a simple metric for describing the composition of igneous rocks, and is related to but distinct from silica content or color index.

Determination of MafikGehalte is usually done by examining a thin section and counting mafic minerals such as olivine, pyroxene, amphibole, and biotite, or through whole-rock analysis using techniques like X-ray fluorescence (XRF) or electron probe microanalysis to quantify mineral proportions. Ultramafic rocks typically show very high MafikGehalte; mafic rocks have moderate to high values; felsic rocks have low values. The value is sometimes integrated with other metrics, such as normative mineralogy.

Classification and interpretation: MafikGehalte helps distinguish rock groups (ultramafic, mafic, intermediate, felsic) and informs about magmatic differentiation and tectonic setting. It correlates with density, color index, and melting history; higher mafic content generally implies higher mantle-derived composition and higher melting temperatures, while lower values indicate crustal differentiation.

Limitations: The concept can be ambiguous because "mafic content" can be defined by different mineral sets, and measurement methods yield different results. Some workers report by weight, others by volume; alteration minerals can bias results. The term is less common in English-language modern petrology, where "mafic content" is preferred, and distinctions between mineralogical content and whole-rock chemical composition are emphasized.

Examples: Ultramafic rocks such as dunite and peridotite have MafikGehalte close to the maximum; basalt and gabbro are mafic; rhyolite and granite are felsic.