Grobkörnung

Grobkörnung is a term used in geology, petrology and soil science to describe materials whose grains are large enough to be seen with the naked eye, in contrast to fine-grained textures where crystals or particles are microscopic. It denotes a textural condition rather than a precise mineral composition.

In igneous rocks, grobkörnig refers to a phaneritic texture formed by slow cooling of magma underground, allowing crystals to grow to millimeter- to centimeter-scale sizes. Common coarse-grained rocks include granite, diorite and gabbro. Porphyritic varieties may display a mix of large phenocrysts set in a finer-grained groundmass, but the overall texture remains grobkörnig. In metamorphic rocks, coarse grains arise from recrystallization at high temperature and pressure, producing sizable minerals in rocks like certain gneisses and schists.

In sedimentology and soil science, grobkörnig describes specimens with substantial content of sand and gravel. Such materials typically exhibit higher porosity and permeability than fine-grained counterparts, and they influence bearing capacity, drainage and compaction behavior. Common coarse fractions include sands and gravels, whose particle sizes are larger than those of silt and clay, though exact boundaries vary by region and standard.

The term is descriptive and context-dependent, and precise grain-size thresholds are not universal. Grobkörnung is primarily used to convey textural and mechanical properties, rather than to fix a strict classification.