Feltspesifikke

Feltspesifikke is a term used in geology, primarily in Norwegian-language texts, to describe rocks or minerals that show a pronounced feldspar content. Feltspat, or feldspar, is the largest mineral group in Earth's crust and includes potassium feldspars (orthoclase, microcline) and the plagioclase series. The adjective feltspesifikke corresponds to the English feldspathic or felsic concept and is used to indicate a composition where feldspar is a dominant framework silicate.

In igneous rocks, feldspathic compositions are common in granitoids and many silica-rich rocks. Granite, granodiorite, and rhyolite are typically described as feldspathic due to their high feldspar and quartz contents, which give them light colors and relatively low density. In sedimentary rocks, feldspar-rich sandstones are termed feldspathic sandstones, and their texture reflects weathering and transport processes that preserve feldspar grains. In metamorphic rocks, feldspar-bearing gneisses and schists are described as feldspathic when feldspar remains a major mineral phase.

Significance: Feldspar content influences rock color, density, and chemical weathering behavior. Feldspathic rocks are generally contrasted with mafic rocks, which contain more pyroxene and amphibole. Analytical methods include modal petrography, X-ray diffraction, and geochemical proxy measures to estimate feldspar abundance and distinguish feldspathic from quartz-rich lithologies.

See also: Feldspar, Feldspathic rock, Granite, Felsic.