Kornstørrelse

Kornstørrelse (grain size) is the diameter of individual particles that make up a material such as soil, sediment, or rock, and the distribution of those diameters within a sample. It is a fundamental descriptor because particle size influences porosity, permeability, strength, and the transport of water, nutrients, and contaminants. Kornstørrelse is typically described by its distribution rather than a single value; common categories in many schemes are gravel, sand, silt, and clay, with multiple subdivisions in more detailed classifications.

Measurement and analysis typically begin with separating the sample into size fractions. Coarser particles are determined by mechanical sieving; finer particles are analyzed by sedimentation methods such as hydrometer or pipette analyses. Modern techniques include laser diffraction and image analysis, which can rapidly yield a detailed grain-size distribution (PSD).

Data from a PSD are often summarized by percentiles such as D10, D50, and D90, which indicate the particle size below which 10, 50, and 90 percent of the sample resides. Sorting describes the spread of sizes; well-sorted materials have a narrow range of particle sizes, poorly sorted materials a wider range.

Scales and nomenclature: The Udden–Wentworth (Wentworth) scale provides standard size classes (gravel, sand, silt, clay) with subdivisions. Other systems, such as ISO 14688/14689 or the Unified Soil Classification System (USCS), use size thresholds to define soil types and textural classes.

Applications and implications: Kornstørrelse affects soil porosity and permeability, infiltration and drainage, bearing capacity, and erosion susceptibility in civil engineering, as well as sediment transport and depositional environments in geology. In rocks, grain size relates to texture—coarse-grained rocks (phaneritic) have visible crystals, while fine-grained rocks (aphanitic) appear uniform at the naked eye.