Movatterモバイル変換

[0]ホーム

Jump to content

Grain size

Edit links

From Wikipedia, the free encyclopedia

Diameter of individual grains of sediment, or of lithified particles in clastic rocks

Not to be confused withcrystallite size, which is referred to as "grain sizes" by metallurgists.

This article includes a list ofgeneral references, butit lacks sufficient correspondinginline citations. Please help toimprove this article byintroducing more precise citations.(July 2011) (Learn how and when to remove this message)

Granulometry

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
v t e

Wentworth grain size chart from United States Geological Survey Open-File Report 2006-1195: Note size typos; 33.1mm is 38.1 & .545mm is .594

Grain size (orparticle size) is thediameter of individual grains ofsediment, or thelithified particles inclastic rocks. The term may also be applied to othergranular materials. This is different from thecrystallite size, which refers to the size of a singlecrystal inside a particle or grain. A single grain can be composed of severalcrystals. Granular material can range from very smallcolloidal particles, throughclay,silt,sand,gravel, andcobbles, toboulders.

Krumbein phi scale

[edit]

Size ranges define limits of classes that are given names in the Wentworth scale (or Udden–Wentworth scale named after geologists Chester K. Wentworth andJohan A. Udden) used in theUnited States. The Krumbeinphi (φ) scale, a modification of the Wentworth scale created byW. C. Krumbein^[1] in 1934, is alogarithmic scale computed by the equation

\varphi =-\log _{2}{\frac {D}{D_{0}}},

where

\varphi

is the Krumbein phi scale,

D {\displaystyle D}

is thediameter of the particle or grain in millimeters (Krumbein and Monk's equation)^[2] and

D_{0}

is a reference diameter, equal to 1 mm (to make the equationdimensionally consistent).

This equation can be rearranged to find diameter using φ:

D=D_{0}\cdot 2^{-\varphi }\,

φ scale	Size range (metric)	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 coarsegravel	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 coarsesand
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	125–250μm	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

[edit]

ISO 14688-1:2017, establishes the basic principles for identifying and classifying soils based on those material and mass characteristics most commonly used for soils for engineering purposes. ISO 14688-1 applies to natural soilsin situ, similar man-made materialsin situ and soils redeposited by people.^[3]

ISO 14688-1:2017
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

Sorting

[edit]

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:^[4]

\sigma _{I}={\frac {\phi 84-\phi 16}{4}}+{\frac {\phi 95-\phi 5}{6.6}}

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:

Diameter (phi units)	Description
$\sigma _{I}$ < 0.35	very well sorted
0.35 < $\sigma _{I}$ < 0.50	well sorted
0.50 < $\sigma _{I}$ < 1.00	moderately sorted
1.00 < $\sigma _{I}$ < 2.00	poorly sorted
2.00 < $\sigma _{I}$ < 4.00	very poorly sorted
4.00 < $\sigma _{I}$	extremely poorly sorted

References

[edit]

^Krumbein, W. C. (1934). "Size frequency distributions of sediments".Journal of Sedimentary Petrology.2 (4).doi:10.1306/D4268EB9-2B26-11D7-8648000102C1865D.
^PetroWiki: Estimating permeability based on grain size
^"ISO 14688-1:2017 – Geotechnical investigation and testing – Identification and classification of soil – Part 1: Identification and description". International Organization for Standardization (ISO).
^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. Archived fromthe original(PDF) on 12 May 2014. Retrieved11 May 2014.

External links

[edit]

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.S2CID 128682870.

v t e Coastal geography
Landforms	Anchialine pool Archipelago Atoll Avulsion Ayre Barrier island Bay Bight Bodden Brackish marsh Cape Channel Cliff Coast Coastal plain Coastal waterfall Continental margin Continental shelf Coral reef Cove Dune cliff-top Estuary Firth Fjard Fjord Freshwater marsh Fundus Gat Geo Gulf Gut Hapua Headland Inlet Intertidal wetland Island Islet Isthmus Liman Lagoon Machair Mudflat Natural arch Peninsula Reef Ria Salt marsh Shoal Skerry Sound Spit Stack Strait Strand plain Submarine canyon Tidal island Tidal marsh Tide pool Tied island Tombolo Waituna Windwatt
Beaches	Beach cusps Beach evolution Beach ridge Beach wrack Beaches in estuaries and bays Beachrock Coastal morphodynamics Pocket beach Raised beach Recession Shell beach Shingle beach Storm beach Wash margin
River mouths	Debouch Mouth bar River delta mega regressive
Processes	Blowhole Cliffed coast Coastal biogeomorphology Coastal erosion Concordant coastline Current Cuspate foreland Discordant coastline Emergent coastline Feeder bluff Flat coast Graded shoreline Ingression coast Large-scale coastal behaviour Longshore drift Marine regression Marine transgression Raised shoreline Rip current Rocky shore Sea cave Sea foam Shoal peresyp Steep coast Submergent coastline Surf break Surf zone Surge channel Swash Undertow Volcanic arc Wave-cut platform Wave shoaling Wind fetch Wind wave
Management	Accretion Coastal management Integrated coastal zone management Submersion
Related	Bulkhead line Coastal engineering Grain size boulder clay cobble granule gravel pebble sand shingle silt Intertidal zone Littoral zone Physical oceanography Region of freshwater influence River plume
Category