Nonclay

Nonclay is a category used in geology and soil science to denote the portion of a soil, sediment, or ceramic body that is not composed of clay minerals. In common practice, soils are described by their mineralogical and textural composition, with the clay fraction defined as minerals with particle sizes smaller than roughly 2 micrometers (and sometimes defined by specific mineral types such as kaolinite, illite, and smectite). The nonclay fraction includes all larger mineral grains—silt, sand, and gravel—as well as non-clay minerals such as quartz, feldspar, calcite, and other minerals that lie outside the clay-size range. Organic matter is typically treated separately from the mineral nonclay fraction in many analyses.

Nonclay minerals influence soil properties differently from clay minerals. They commonly govern bulk density, permeability, bearing capacity, and sediment strength, and they can affect how soils compact, drain, and shear. In engineering and construction, the proportion of nonclay material helps determine suitable uses and stabilization requirements for soils and aggregates.

Analytical approaches to quantify nonclay content include gravimetric sieving and sedimentation to separate particle sizes, as well as X-ray diffraction and other mineralogical techniques to identify specific nonclay minerals. Because the boundary between clay and nonclay fractions is method-dependent, definitions of nonclay may vary by discipline and region.

See also: clay mineral, soil texture, sedimentology, mineralogy, geotechnical engineering.