Grain size

Grain size (or particle size) is the diameter of individual grains of sediment, or the lithified particles in clastic rocks. The term may also be applied to other granular materials. This is different from the crystallite size, which refers to the size of a single crystal inside a particle or grain. A single grain can be composed of several crystals. Granular material can range from very small colloidal particles, through clay, silt, sand, gravel, and cobbles, to boulders.

Sample Net-withGraphic
Basic concepts
Particle size · Grain size
Size distribution · Morphology
Methods and techniques
Mesh scale · Optical granulometry
Sieve analysis · Soil gradation

Related concepts
Granulation · Granular material
Mineral dust · Pattern recognition
Dynamic light scattering
Wentworth scale
Wentworth grain size chart from United States Geological Survey Open-File Report 2006-1195
Cobbles Nash Point
Beach cobbles at Nash Point, South Wales.

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 Krumbein phi (φ) scale, a modification of the Wentworth scale created by W. C. Krumbein[1] in 1934, is a logarithmic scale computed by the equation


is the Krumbein phi scale,
is the diameter of the particle or grain in millimeters (from petrowiki, krumbein and monks equation) and
is a reference diameter, equal to 1 mm (to make the equation dimensionally consistent).

This equation can be rearranged to find diameter using φ:

φ scale Size range
Size range
(approx. inches)
Aggregate name
(Wentworth class)
Other names
<−8 >256 mm >10.1 in Boulder
−6 to −8 64–256 mm 2.5–10.1 in Cobble
−5 to −6 32–64 mm 1.26–2.5 in Very coarse gravel Pebble
−4 to −5 16–32 mm 0.63–1.26 in Coarse gravel Pebble
−3 to −4 8–16 mm 0.31–0.63 in Medium gravel Pebble
−2 to −3 4–8 mm 0.157–0.31 in Fine gravel Pebble
−1 to −2 2–4 mm 0.079–0.157 in Very fine gravel Granule
0 to −1 1–2 mm 0.039–0.079 in Very coarse sand
1 to 0 0.5–1 mm 0.020–0.039 in Coarse sand
2 to 1 0.25–0.5 mm 0.010–0.020 in Medium sand
3 to 2 125–250 µm 0.0049–0.010 in Fine sand
4 to 3 62.5–125 µm 0.0025–0.0049 in Very fine sand
8 to 4 3.9–62.5 µm 0.00015–0.0025 in Silt Mud
10 to 8 0.98–3.9 µm 3.8×10−5–0.00015 in Clay Mud
20 to 10 0.95–977 nm 3.8×10−8–3.8×10−5 in Colloid Mud

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.[2]

ISO 14688-1:2002
Name Size range (mm) Size range (approx. in)
Very coarse soil Large boulder LBo >630 >24.8031
Boulder Bo 200–630 7.8740–24.803
Cobble Co 63–200 2.4803–7.8740
Coarse soil Gravel Coarse gravel CGr 20–63 0.78740–2.4803
Medium gravel MGr 6.3–20 0.24803–0.78740
Fine gravel FGr 2.0–6.3 0.078740–0.24803
Sand Coarse sand CSa 0.63–2.0 0.024803–0.078740
Medium sand MSa 0.2–0.63 0.0078740–0.024803
Fine sand FSa 0.063–0.2 0.0024803–0.0078740
Fine soil Silt Coarse silt CSi 0.02–0.063 0.00078740–0.0024803
Medium silt MSi 0.0063–0.02 0.00024803–0.00078740
Fine silt FSi 0.002–0.0063 0.000078740–0.00024803
Clay Cl ≤0.002 ≤0.000078740


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:[3]


is the Inclusive Graphic Standard Deviation in phi units
is the 84th percentile of the grain size distribution in phi units, etc.

The result of this can be described using the following terms:

Diameter (phi units) Description
< 0.35 very well sorted
0.35 < < 0.50 well sorted
0.50 < < 1.00 moderately sorted
1.00 < < 2.00 poorly sorted
2.00 < < 4.00 very poorly sorted
4.00 < extremely poorly sorted

See also


  1. ^ Krumbein, W. C. (1934). "Size frequency distributions of sediments". Journal of Sedimentary Petrology. 2 (4). doi:10.1306/D4268EB9-2B26-11D7-8648000102C1865D. Retrieved 11 May 2014. (Subscription required (help)). Cite uses deprecated parameter |subscription= (help)
  2. ^ "ISO 14688-1:2002 – Geotechnical investigation and testing – Identification and classification of soil – Part 1: Identification and description". International Organization for Standardization (ISO).
  3. ^ Folk, Robert L.; Ward, William C. (1957). "Brazos River bar: a study in the significance of grain-size parameters" (PDF). Journal of Sedimentary Petrology. 27 (1): 3–26. Bibcode:1957JSedR..27....3F. doi:10.1306/74d70646-2b21-11d7-8648000102c1865d. Retrieved 11 May 2014.

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).
  • Udden, J. A. (1914). "Mechanical composition of clastic sediments". Geological Society of America Bulletin. 25 (1): 655–744. Bibcode:1914GSAB...25..655U. doi:10.1130/GSAB-25-655.
  • Wentworth, C. K. (1922). "A Scale of Grade and Class Terms for Clastic Sediments". The Journal of Geology. 30 (5): 377–392. Bibcode:1922JG.....30..377W. doi:10.1086/622910. JSTOR 30063207.
Annealing (metallurgy)

In metallurgy and materials science, annealing is a heat treatment that alters the physical and sometimes chemical properties of a material to increase its ductility and reduce its hardness, making it more workable. It involves heating a material above its recrystallization temperature, maintaining a suitable temperature for a suitable amount of time, and then cooling.

In annealing, atoms migrate in the crystal lattice and the number of dislocations decreases, leading to a change in ductility and hardness. As the material cools it recrystallizes. For many alloys, including carbon steel, the crystal grain size and phase composition, which ultimately determine the material properties, are dependent on the heating rate and cooling rate. Hot working or cold working after the annealing process alter the metal structure, so further heat treatments may be used to achieve the properties required. With knowledge of the composition and phase diagram, heat treatment can be used to adjust from harder and more brittle to softer and more ductile.

In the cases of copper, steel, silver, and brass, this process is performed by heating the material (generally until glowing) for a while and then slowly letting it cool to room temperature in still air. Copper, silver and brass can be cooled slowly in air, or quickly by quenching in water, unlike ferrous metals, such as steel, which must be cooled slowly to anneal. In this fashion, the metal is softened and prepared for further work such as shaping, stamping, or forming.


A material is brittle if, when subjected to stress, it breaks without significant plastic deformation. Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Breaking is often accompanied by a snapping sound. Brittle materials include most ceramics and glasses (which do not deform plastically) and some polymers, such as PMMA and polystyrene. Many steels become brittle at low temperatures (see ductile-brittle transition temperature), depending on their composition and processing.

When used in materials science, it is generally applied to materials that fail when there is little or no plastic deformation before failure. One proof is to match the broken halves, which should fit exactly since no plastic deformation has occurred.

When a material has reached the limit of its strength, it usually has the option of either deformation or fracture. A naturally malleable metal can be made stronger by impeding the mechanisms of plastic deformation (reducing grain size, precipitation hardening, work hardening, etc.), but if this is taken to an extreme, fracture becomes the more likely outcome, and the material can become brittle. Improving material toughness is therefore a balancing act.

Deposition (geology)

Deposition is the geological process in which sediments, soil and rocks are added to a landform or land mass. Wind, ice, water, and gravity transport previously weathered surface material, which, at the loss of enough kinetic energy in the fluid, is deposited, building up layers of sediment.

Deposition occurs when the forces responsible for sediment transportation are no longer sufficient to overcome the forces of gravity and friction, creating a resistance to motion; this is known as the null-point hypothesis. Deposition can also refer to the buildup of sediment from organically derived matter or chemical processes. For example, chalk is made up partly of the microscopic calcium carbonate skeletons of marine plankton, the deposition of which has induced chemical processes (diagenesis) to deposit further calcium carbonate. Similarly, the formation of coal begins with deposition of organic material, mainly from plants, in anaerobic conditions.


Flagstone (flag) is a generic flat stone, cutting regular rectangular or square in shape and usually used for paving slabs or walkways, patios, flooring, fences and roofing. It may be used for memorials, headstones, facades and other construction. The name derives from Middle English flagge meaning turf, perhaps from Old Norse flaga meaning slab or chip.

Flagstone is a sedimentary rock that is split into layers along bedding planes. Flagstone is usually a form of a sandstone composed of feldspar and quartz and is arenaceous in grain size (0.16 mm – 2 mm in diameter). The material that binds flagstone is usually composed of silica, calcite, or iron oxide. The rock color usually comes from these cementing materials. Typical flagstone colors are red, blue, and buff, though exotic colors exist.

Flagstone is quarried in places with bedded sedimentary rocks with fissile bedding planes.

Around the thirteenth century, the ceilings, walls and floors in European architecture became more ornate. Anglo-Saxons in particular used flagstones as flooring materials in the interior rooms of castles and other structures.Lindisfarne Castle in England and Muchalls Castle (14th century) in Scotland are among many examples of buildings with surviving flagstone floors.

Flagstone shingles are a traditional roofing material, a type of roof shingle commonly used in the Alps, where they are laid dry, often held in place with pegs or hooks. In the Aosta Valley, Italy, stone shingles are mandatory to cover buildings in historical areas.

Grain boundary strengthening

Grain-boundary strengthening (or Hall–Petch strengthening) is a method of strengthening materials by changing their average crystallite (grain) size. It is based on the observation that grain boundaries are insurmountable borders for dislocations and that the number of dislocations within a grain have an effect on how stress builds up in the adjacent grain, which will eventually activate dislocation sources and thus enabling deformation in the neighbouring grain, too. So, by changing grain size one can influence the number of dislocations piled up at the grain boundary and yield strength. For example, heat treatment after plastic deformation and changing the rate of solidification are ways to alter grain size.

ISO 6344

ISO 6344 is an international standard covering the materials sizes and tests regarding sandpaper and other similar coated abrasives.

It has three parts:

ISO 6344-1:1998: Grain size distribution test

ISO 6344-2:1998: Determination of grain size distribution of macrogrits P12 to P220

ISO 6344-3:1998: Determination of grain size distribution of microgrits P240 to P2500

Korean brining salt

Korean brining salt, also called Korean sea salt, is a variety of edible salt with a larger grain size compared to common kitchen salt. It is called wang-sogeum (왕소금; "king/queen salt") or gulgeun-sogeum (굵은소금; "coarse salt") in Korean. The salt is used mainly for salting napa cabbages when making kimchi. Being minimally processed, it serves to help developing flavours in fermented foods.


The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain size, and composition. Lithology may refer to either a detailed description of these characteristics, or a summary of the gross physical character of a rock. Lithology is the basis of subdividing rock sequences into individual lithostratigraphic units for the purposes of mapping and correlation between areas. In certain applications, such as site investigations, lithology is described using a standard terminology such as in the European geotechnical standard Eurocode 7.


A micrograph or photomicrograph is a photograph or digital image taken through a microscope or similar device to show a magnified image of an object. This is opposed to a macrograph or photomacrograph, an image which is also taken on a microscope but is only slightly magnified, usually less than 10 times. Micrography is the practice or art of using microscopes to make photographs.

A micrograph contains extensive details of microstructure. A wealth of information can be obtained from a simple micrograph like behavior of the material under different conditions, the phases found in the system, failure analysis, grain size estimation, elemental analysis and so on. Micrographs are widely used in all fields of microscopy.

Mill (grinding)

A mill is a device that breaks solid materials into smaller pieces by grinding, crushing, or cutting. Such comminution is an important unit operation in many processes. There are many different types of mills and many types of materials processed in them. Historically mills were powered by hand (e.g., via a hand crank), working animal (e.g., horse mill), wind (windmill) or water (watermill). Today they are usually powered by electricity.

The grinding of solid materials occurs through mechanical forces that break up the structure by overcoming the interior bonding forces. After the grinding the state of the solid is changed: the grain size, the grain size disposition and the grain shape.

Milling also refers to the process of breaking down, separating, sizing, or classifying aggregate material. For instance rock crushing or grinding to produce uniform aggregate size for construction purposes, or separation of rock, soil or aggregate material for the purposes of structural fill or land reclamation activities. Aggregate milling processes are also used to remove or separate contamination or moisture from aggregate or soil and to produce "dry fills" prior to transport or structural filling.

Grinding may serve the following purposes in engineering:

increase of the surface area of a solid

manufacturing of a solid with a desired grain size

pulping of resources


Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Grain size is up to 0.063 millimetres (0.0025 in) with individual grains too small to be distinguished without a microscope. With increased pressure over time, the platy clay minerals may become aligned, with the appearance of fissility or parallel layering. This finely bedded material that splits readily into thin layers is called shale, as distinct from mudstone. The lack of fissility or layering in mudstone may be due to either original texture or the disruption of layering by burrowing organisms in the sediment prior to lithification. Mud rocks such as mudstone and shale account for some 65% of all sedimentary rocks. Mudstone looks like hardened clay and, depending upon the circumstances under which it was formed, it may show cracks or fissures, like a sun-baked clay deposit.Mudstone can be separated into these categories:

Siltstone — more than half of the composition is silt-sized particles.

Claystone — more than half of the composition is clay-sized particles.

Mudstone — hardened mud; a mix of silt and clay sized particles. Mudstone can include:

Shale — exhibits lamination or fissility.

Argillite — has undergone low-grade metamorphism.

Nanocrystalline material

A nanocrystalline (NC) material is a polycrystalline material with a crystallite size of only a few nanometers. These materials fill the gap between amorphous materials without any long range order and conventional coarse-grained materials. Definitions vary, but nanocrystalline material is commonly defined as a crystallite (grain) size below 100 nm. Grain sizes from 100–500 nm are typically considered "ultrafine" grains.

The grain size of a NC sample can be estimated using x-ray diffraction. In materials with very small grain sizes, the diffraction peaks will be broadened. This broadening can be related to a crystallite size using the Scherrer equation (applicable up to ~50 nm), a Williamson-Hall plot, or more sophisticated methods such as the Warren-Averbach method or computer modeling of the diffraction pattern. The crystallite size can be measured directly using transmission electron microscopy.

Particle-size distribution

The particle-size distribution (PSD) of a powder, or granular material, or particles dispersed in fluid, is a list of values or a mathematical function that defines the relative amount, typically by mass, of particles present according to size. Significant energy is usually required to disintegrate soil, etc. particles into the PSD that is then called a grain size distribution.


Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand and silt can be carried in suspension in river water and on reaching the sea bed deposited by sedimentation. If buried, they may eventually become sandstone and siltstone (sedimentary rocks) through lithification.

Sediments are most often transported by water (fluvial processes), but also wind (aeolian processes) and glaciers. Beach sands and river channel deposits are examples of fluvial transport and deposition, though sediment also often settles out of slow-moving or standing water in lakes and oceans. Desert sand dunes and loess are examples of aeolian transport and deposition. Glacial moraine deposits and till are ice-transported sediments.


Silt is granular material of a size between sand and clay, whose mineral origin is quartz and feldspar. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water (also known as a suspended load) and soil in a body of water such as a river. It may also exist as soil deposited at the bottom of a water body, like mudflows from landslides. Silt has a moderate specific area with a typically non-sticky, plastic feel. Silt usually has a floury feel when dry, and a slippery feel when wet. Silt can be visually observed with a hand lens, exhibiting a sparkly appearance. It also can be felt by the tongue as granular when placed on the front teeth (even when mixed with clay particles).


Siltstone is a sedimentary rock which has a grain size in the silt range, finer than sandstone and coarser than claystones.

Subvolcanic rock

A subvolcanic rock, also known as a hypabyssal rock, is an intrusive igneous rock that is emplaced at medium to shallow depths (>2 km) within the crust, and has intermediate grain size and often porphyritic texture between that of volcanic rocks and plutonic rocks. Subvolcanic rocks include diabase (also known as dolerite) and porphyry.

Common examples of subvolcanic rocks are diabase, quartz-dolerite, micro-granite and diorite.

Unified Soil Classification System

The Unified Soil Classification System (USCS) is a soil classification system used in engineering and geology to describe the texture and grain size of a soil. The classification system can be applied to most unconsolidated materials, and is represented by a two-letter symbol. Each letter is described below (with the exception of Pt):

If the soil has 5–12% by weight of fines passing a #200 sieve (5% < P#200 < 12%), both grain size distribution and plasticity have a significant effect on the engineering properties of the soil, and dual notation may be used for the group symbol. For example, GW-GM corresponds to "well-graded gravel with silt."

If the soil has more than 15% by weight retained on a #4 sieve (R#4 > 15%), there is a significant amount of gravel, and the suffix "with gravel" may be added to the group name, but the group symbol does not change. For example, SP-SM could refer to "poorly graded SAND with silt" or "poorly graded SAND with silt and gravel."



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