lerfraktioner

Lerfraktioner, in English often translated as clay fractions, refers to the clay-sized mineral components that make up a soil or sediment. The term encompasses both the size-based definition of clay particles—generally those smaller than about 0.002 millimeters (2 micrometers)—and the mineralogical composition of that fraction, which is typically dominated by clay minerals such as kaolinite, illite, smectite (montmorillonite), chlorite, vermiculite, and various mixed-layer clays.

Why it matters: The clay fraction strongly influences soil texture, plasticity, and shrink-swell behavior, as well as water retention and nutrient holding capacity (cation exchange capacity). The mineralogy of the lerfraktioner controls properties such as plasticity, hydraulic conductivity, and fertility, since different minerals have different surface areas and exchange characteristics.

How it is analyzed: Determination of clay fractions involves size separation techniques, such as sedimentation using the hydrometer or pipette method, to isolate particles in the clay size class. Mineralogical composition is commonly determined with X-ray diffraction (XRD), sometimes complemented by infrared spectroscopy or selective chemical dissolution to distinguish expandable and non-expandable clays.

Applications: In pedology, lerfraktioner inform soil classification, weathering intensity, and long-term behavior under cultivation. In geology and sedimentology, clay mineralogy helps reconstruct depositional environments and source rock weathering.

Limitations: Clay fractions can be heterogeneous within a sample, and preparation or analysis conditions can bias results; mixed-layer and expanding clays may complicate interpretation. Care is required when comparing results from different laboratories.