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Grain size (or particle size) is the
diameter In geometry Geometry (from the grc, γεωμετρία; ''wikt:γῆ, geo-'' "earth", ''wikt:μέτρον, -metron'' "measurement") is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space t ...
of individual grains of
sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently sediment transport, transported by the action of wind, water, or ice or by the force of gravity acting on the particles. Fo ...
, or the lithified particles in clastic rocks. The term may also be applied to other granular materials. This is different from the
crystallite A crystallite is a small or even microscopic crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice ...
size, which refers to the size of a single
crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macrosco ...
inside a particle or grain. A single grain can be composed of several
crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macrosco ...
s. Granular material can range from very small colloidal particles, through
clay Clay is a type of fine-grained natural soil material containing clay minerals. Clays develop plasticity (physics), plasticity when wet, due to a molecular film of water surrounding the clay particles, but become hard, brittle and non–plastic ...

clay
, silt, sand, gravel, and cobbles, to
boulder
boulder
s.


Krumbein phi scale

Size ranges define limits of classes that are given names in the Wentworth scale (or Udden–Wentworth scale) used in the
United States The United States of America (USA), commonly known as the United States (U.S. or US), or America, is a country Contiguous United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., federal di ...
. The Krumbein ''phi'' (φ) scale, a modification of the Wentworth scale created by W. C. Krumbein in 1934, is a
logarithmic scaleA logarithmic scale (or log scale) is a way of displaying numerical data over a very wide range of values in a compact way—typically the largest numbers in the data are hundreds or even thousands of times larger than the smallest numbers. Such a sc ...

logarithmic scale
computed by the equation :\varphi=-\log_2, where :\varphi is the Krumbein phi scale, :D is the
diameter In geometry Geometry (from the grc, γεωμετρία; ''wikt:γῆ, geo-'' "earth", ''wikt:μέτρον, -metron'' "measurement") is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space t ...
of the particle or grain in millimeters (Krumbein and Monk's equation)PetroWiki: Estimating permeability based on grain size
/ref> and :D_0 is a reference diameter, equal to 1 mm (to make the equation dimensionally consistent). This equation can be rearranged to find diameter using φ: :D=D_0 \cdot 2^\, In some schemes, gravel is anything larger than sand (comprising granule, pebble, cobble, and boulder in the table above).


International scale

ISO 14688-1:2002, establishes the basic principles for the identification and classification of soils on the basis of those material and mass characteristics most commonly used for soils for engineering purposes. ISO 14688-1 is applicable to natural soils ''in situ'', similar man-made materials ''in situ'' and soils redeposited by people.


Sorting

An accumulation of sediment can also be characterized by the grain size distribution. A sediment deposit can undergo sorting when a particle size range is removed by an agency such as a river or the wind. The sorting can be quantified using the Inclusive Graphic Standard Deviation: :\sigma_I=\frac + \frac where :\sigma_I is the Inclusive Graphic Standard Deviation in phi units :\phi 84 is the 84th percentile of the grain size distribution in phi units, etc. The result of this can be described using the following terms:


See also

* Feret diameter * Martin diameter * Orders of magnitude (volume) * Soil texture * Substrate (biology) * Unified Soil Classification System (USCS)


References


External links

* R D Dean & R A Dalrymple, ''Coastal Processes with Engineering Applications'' (Cambridge University Press, 2002) * W C Krumbein & L L Sloss, ''Stratigraphy and Sedimentation'', 2nd edition (Freeman, San Francisco, 1963). * * {{coastal geography Sedimentary rocks Pedology