Editing Gravel

{{Short description|Mix of crumbled stones: grain size range between 2 – 63 mm according to ISO 14688}}
{{Other uses}}
{{Use dmy dates|date=November 2021}}
[[File:Gravel on a beach in Thirasia, Santorini, Greece.jpg|thumb|upright=1.35|Gravel (largest fragment in this photo is about {{cvt|40|mm|in}})]]

'''Gravel''' ({{IPAc-en|ˈ|ɡ|r|æ|v|əl}}) is a loose aggregation of [[rock fragment]]s. Gravel occurs naturally on [[Earth]] as a result of [[sedimentation|sedimentary]] and [[erosion|erosive]] geological processes; it is also produced in large quantities commercially as [[crushed stone]].

Gravel is classified by [[grain size|particle size]] range and includes size classes from [[granule (geology)|granule]]- to [[boulder]]-sized fragments. In the [[grain size|Udden-Wentworth scale]] gravel is categorized into granular gravel ({{cvt|2–4|mm|in|disp=or}}) and [[pebble]] gravel ({{cvt|4–64|mm|in|1|disp=or}}). ISO 14688 grades gravels as fine, medium, and coarse, with ranges {{cvt|2–6.3|mm|in}} for fine and {{cvt|20–63|mm|in}} for coarse. One [[cubic metre]] of gravel typically weighs about {{cvt|1,800|kg|lb}}, or one [[cubic yard]] weighs about {{cvt|3,000|lb|kg}}.

Gravel is an important commercial product, with a number of applications. Almost half of all gravel production is used as [[construction aggregate|aggregate]] for [[concrete]]. Much of the rest is used for road construction, either in the road base or as the road surface (with or without [[bitumen|asphalt]] or other binders.) Naturally occurring porous gravel deposits have a high [[hydraulic conductivity]], making them important [[aquifer]]s.

==Definition and properties==
[[File:Kiesgrube Bernau 2012 - panoramio (7).jpg|thumb|Sand and gravel separator in a gravel pit in Germany]]

Colloquially, the term gravel is often used to describe a mixture of different size pieces of stone mixed with sand and possibly some clay.<ref>{{cite OED|gravel}}</ref> The American construction industry distinguishes between gravel (a natural material) and [[crushed stone]] (produced artificially by mechanical crushing of rock.)<ref>{{cite journal |last1=Dolley |first1=Thomas P. |title=Sand and gravel (construction) |journal=U.S. Geological Survey Mineral Commodies Summary |date=2021 |page=141 |doi=10.3133/mcs2021 |s2cid=242973747 |doi-access=free }}</ref><ref>{{cite web |title=The complete guide to crushed stone and gravel |url=https://www.gra-rock.com/post/2019/11/11/the-complete-beginners-guide-to-crushed-stone-and-gravel |website=Gra-Rock |access-date=24 November 2021 |date=16 June 2020}}</ref><ref>{{cite web |title=Crushed stone vs. gravel |url=https://alblairconstruction.com/crushed-stone-vs-gravel/ |website=A.L.Blair Construction Ltd. |date=24 October 2017 |access-date=24 November 2021}}</ref>

The technical definition of gravel varies by region and by area of application. Many geologists define gravel simply as loose rounded rock particles over {{cvt|2|mm|in|sp=us}} in diameter, without specifying an upper size limit.<ref name=Jackson/><ref name=BlattTracy>{{cite book |last1=Blatt |first1=Harvey |last2=Tracy |first2=Robert J. |title=Petrology : igneous, sedimentary, and metamorphic. |date=1996 |publisher=W.H. Freeman |location=New York |isbn=0716724383 |edition=2nd |page=523}}</ref><ref name=Boggs>{{cite book |last1=Boggs |first1=Sam |title=Principles of sedimentology and stratigraphy |date=2006 |publisher=Pearson Prentice Hall |location=Upper Saddle River, N.J. |isbn=0131547283 |edition=4th |page=135}}</ref><ref name=Allaby>{{cite book |last1=Allaby |first1=Michael |title=A dictionary of geology and earth sciences |date=2013 |publisher=Oxford University Press |location=Oxford |isbn=9780199653065 |edition=Fourth |chapter=gravel}}</ref> Gravel is sometimes distinguished from rubble, which is loose rock particles in the same size range but angular in shape.<ref>{{cite book |last1=Prothero |first1=Donald R. |last2=Schwab |first2=Fred |title=Sedimentary geology : an introduction to sedimentary rocks and stratigraphy |date=2004 |publisher=W.H. Freeman |location=New York |isbn=0-7167-3905-4 |page=67 |edition=2nd}}</ref> The [[Udden-Wentworth scale]], widely used by geologists in the US, defines granular gravel as particles with a size from {{cvt|2 to 4|mm|in|sp=us}} and pebble gravel as particles with a size from {{cvt|4 to 64|mm|in|sp=us}}. This corresponds to all particles with sizes between coarse [[sand]] and [[cobble (geology)|cobbles]].<ref>{{cite journal |title=Size frequency distributions of sediments |last=Krumbein |first=W. C. |date=1934 |journal=Journal of Sedimentary Petrology |issue=4 |volume=2 |doi=10.1306/D4268EB9-2B26-11D7-8648000102C1865D}}</ref>

The [[U.S. Department of Agriculture]] and the [[Soil Science Society of America]] define gravel as particles from {{cvt|2 to 80|mm|in|sp=us}} in size, while the German scale (Atterburg) defines gravel as particles from {{cvt|2 to 200|mm|in|sp=us}} in size.<ref name="blatt-etal-1980">{{cite book |last1=Blatt |first1=Harvey |last2=Middletone |first2=Gerard |last3=Murray |first3=Raymond |title=Origin of sedimentary rocks |date=1980 |publisher=Prentice-Hall |location=Englewood Cliffs, N.J. |isbn=0136427103 |page=57 |edition=2d}}</ref> The [[U.S. Army Corps of Engineers]] defines gravel as particles under {{cvt|3|in|mm|sp=us}} in size that are retained by a number 4 mesh, which has a mesh spacing of {{cvt|4.76|mm|in|sp=us}}.<ref name="blatt-etal-1980-629-632">{{cite book |last1=Blatt |first1=Harvey |last2=Middletone |first2=Gerard |last3=Murray |first3=Raymond |title=Origin of sedimentary rocks |date=1980 |publisher=Prentice-Hall |location=Englewood Cliffs, N.J. |isbn=0136427103 |page=631 |edition=2d}}</ref><ref name=Jackson>{{cite book |editor1-last=Jackson |editor1-first=Julia A. |title=Glossary of geology. |date=1997 |publisher=American Geological Institute |location=Alexandria, Virginia |isbn=0922152349 |edition=Fourth |chapter=gravel}}</ref> ISO 14688 for [[soil engineering]] grades gravels as fine, medium, and coarse with ranges 2&nbsp;mm to 6.3&nbsp;mm to 20&nbsp;mm to 63&nbsp;mm.<ref name=ISO>{{cite web |url=https://www.iso.org/standard/66345.html |title=ISO 14688-1:2002 – Geotechnical investigation and testing – Identification and classification of soil – Part 1: Identification and description |publisher=[[International Organization for Standardization|ISO]]}}</ref>

The [[bulk density]] of gravel varies from {{cvt|1460 to 1920|kg/m3||sp=us}}.<ref>{{cite book |editor-last1=Hartman |editor-first1=H L. |year=1992 |title=Society for mining, metallurgy and exploration (SME) Mining Engineering Handbook |edition=2nd |volume=2 |publisher=Society for mining, metallurgy and exploration (SME) |location=Littleton, Colorado, USA |isbn=978-0873351003}}</ref> Natural gravel has a high [[hydraulic conductivity]], sometimes reaching above 1&nbsp;cm/s.<ref>{{Cite book|last=Freeze, R. Allan|url=https://www.worldcat.org/oclc/4493153|title=Groundwater|date=1979|publisher=Prentice-Hall|others=Cherry, John A.|isbn=0-13-365312-9|location=Englewood Cliffs, N.J.|oclc=4493153}}</ref>

==Origin==
Most gravel is derived from disintegration of [[bedrock]] as it [[Weathering|weathers]]. [[Quartz]] is the most common [[mineral]] found in gravel, as it is hard, chemically inert, and lacks [[cleavage plane]]s along which the rock easily splits. Most gravel particles consist of multiple [[mineral]] grains, since few rocks have mineral grains coarser than about {{convert|8|mm||sp=us}} in size. Exceptions include quartz [[Vein (geology)|veins]], [[pegmatite]]s, deep [[intrusion]]s, and high-grade [[metamorphic rock]]. The rock fragments are rapidly rounded as they are transported by [[river]]s, often within a few tens of kilometers of their source outcrops.{{sfn|Prothero|Schwab|2004|pp=68-70}}

Gravel is deposited as gravel blankets or bars in stream channels;{{sfn|Prothero|Schwab|2004|p=74}} in [[alluvial fans]];<ref name="leeder-2011-282-294"/> in near-shore marine settings, where the gravel is supplied by streams or erosion along the coast;<ref>{{cite journal |last1=Jennings |first1=S. |last2=Smyth |first2=C. |title=Holocene evolution of the gravel coastline of East Sussex |journal=Proceedings of the Geologists' Association |date=January 1990 |volume=101 |issue=3 |pages=213–224 |doi=10.1016/S0016-7878(08)80006-5|bibcode=1990PrGA..101..213J }}</ref><ref>{{cite journal |last1=Bridgland |first1=D. R. |last2=Saville |first2=A. |last3=Sinclair |first3=J. M. |title=New evidence for the origin of the Buchan Ridge Gravel, Aberdeenshire |journal=Scottish Journal of Geology |date=June 1997 |volume=33 |issue=1 |pages=43–50 |doi=10.1144/sjg33010043|bibcode=1997ScJG...33...43B |s2cid=129225730 }}</ref>{{sfn|Prothero|Schwab|2004|p=74}} and in the deltas of swift-flowing streams.<ref>{{cite journal |last1=Cary |first1=Allen S. |title=Origin and Significance of Openwork Gravel |journal=Transactions of the American Society of Civil Engineers |date=January 1951 |volume=116 |issue=1 |pages=1296–1308 |doi=10.1061/TACEAT.0006486}}</ref> The upper [[Mississippi embayment]] contains extensive [[chert]] gravels thought to have their origin less than {{convert|100|mi||sp=us}} from the periphery of the embayment.<ref>{{cite journal |last1=Potter |first1=Paul Edwin |title=The Petrology and Origin of the Lafayette Gravel: Part 1. Mineralogy and Petrology |journal=The Journal of Geology |date=January 1955 |volume=63 |issue=1 |pages=1–38 |doi=10.1086/626223|bibcode=1955JG.....63....1P |s2cid=128550835 }}</ref>

It has been suggested that wind-formed ([[Aeolian processes|aeolian]]) gravel "megaripples" in [[Argentina]] have counterparts on the planet [[Mars]].<ref>{{cite journal |last1=de Silva |first1=S. L. |last2=Spagnuolo |first2=M. G. |last3=Bridges |first3=N. T. |last4=Zimbelman |first4=J. R. |title=Gravel-mantled megaripples of the Argentinean Puna: A model for their origin and growth with implications for Mars |journal=Geological Society of America Bulletin |date=1 November 2013 |volume=125 |issue=11–12 |pages=1912–1929 |doi=10.1130/B30916.1|bibcode=2013GSAB..125.1912D }}</ref>

==Production and uses==
[[File:Soratie Kalkkinen.jpg|thumb|A [[gravel road]] in Finland]]

Gravel is a major basic raw material in [[construction]].<ref name=Bolen>{{cite journal |last1=Bolen |first1=W.P. |year=2000 |title=Sand and gravel construction |journal=US Geological Survey Minerals Yearbook |url=http://prd-wret.s3.amazonaws.com/assets/palladium/production/mineral-pubs/sand-gravel-construction/590400.pdf |access-date=26 July 2021 |archive-date=20 October 2021 |archive-url=https://web.archive.org/web/20211020223023/http://prd-wret.s3.amazonaws.com/assets/palladium/production/mineral-pubs/sand-gravel-construction/590400.pdf |url-status=dead }}</ref> Sand is not usually distinguished from gravel in official statistics, but [[crushed stone]] is treated as a separate category. In 2020, sand and gravel together made up 23% of all industrial mineral production in the U.S., with a total value of about $12.6 billion. Some 960 million tons of construction sand and gravel were produced. This greatly exceeds production of industrial sand and gravel (68 million tons), which is mostly sand rather than gravel.<ref name=USGS>{{cite report |last1=U.S. Geological Survey |title=Mineral Commodity Summaries |date=2021 |doi=10.3133/mcs2021 |pages=141–143 |doi-access=free }}</ref>

It is estimated that almost half of construction sand and gravel is used as [[Construction aggregate|aggregate]] for [[concrete]]. Other important uses include in road construction, as road base or in [[blacktop]]; as construction fill; and in myriad minor uses.<ref name=Bolen/>

Gravel is widely and plentifully distributed, mostly as river deposits, river flood plains, and glacial deposits, so that environmental considerations and quality dictate whether alternatives, such as [[crushed stone]], are more economical. Crushed stone is already displacing natural gravel in the eastern United States, and recycled gravel is also becoming increasingly important.<ref name=USGS/>

==Etymology==
The word ''gravel'' comes from the [[Old French]] ''gravele''<ref>Collins English Dictionary – Complete & Unabridged 11th Edition. Retrieved 30 August 2012 from CollinsDictionary.com website:http://www.collinsdictionary.com/dictionary/english/gravel</ref> or ''gravelle''.<ref>Gravel, n., ''Oxford English Dictionary'' Second Edition on CD-ROM (v. 4.0) © Oxford University Press 2009</ref>

==Types==
[[File:Varieties of Gravel in different shapes and size. 01.jpg|thumb|upright|Naturally occurring sedimentary gravel bed]]
[[File:Gravel small stones.jpg|thumb|Graded mechanically [[crushed stone]], with particle sizes roughly between 5 and 15 mm]]

Different varieties of gravel are distinguished by their composition, origin, and use cases. Types of gravel include:

;Bank gravel: naturally deposited gravel intermixed with sand or [[clay]] found in and next to rivers and streams.  Also known as "bank run" or "river run".{{sfn|Jackson|1997|loc="bank gravel"}}
;Bench gravel: a bed of gravel located on the side of a valley above the present stream bottom, indicating the former location of the stream bed when it was at a higher level. The term is most commonly used in [[Alaska]] and the [[Yukon Territory]].{{sfn|Jackson|1997|loc="bench gravel"}}
;[[Crushed stone]]: rock crushed and graded by screens and then mixed to a blend of stones and fines. It is widely used as a surfacing for roads and driveways, sometimes with [[tar]] applied over it. Crushed stone may be made from [[granite]], [[limestone]], [[Dolomite (rock)|dolomite]], and other rocks. Also known as "crusher run", DGA (dense grade aggregate) QP (quarry process), and shoulder stone.<ref>{{cite web|url=http://www.braenstone.com/crushed-stone/quarry-process-qp-dga/|title=Quarry Process – QP, DGA – NJ, NY, NYC, PA|website=braenstone.com|access-date=1 May 2014|archive-date=27 January 2018|archive-url=https://web.archive.org/web/20180127202621/https://www.braenstone.com/crushed-stone/quarry-process-qp-dga/|url-status=dead}}</ref> Crushed stone is distinguished from gravel by the U.S. Geological Survey.<ref name=USGS/>
;Fine gravel: gravel consisting of particles with a diameter of {{convert|2 to 6.3|mm}}<ref name=ISO/>
;[[Lag deposit|Lag gravel]]: a surface accumulation of coarse gravel produced by the removal of finer particles.
;Pay gravel: also known as "pay dirt"; a nickname for gravel with a high concentration of gold and other precious metals. The metals are recovered through [[gold panning]].
;Pea gravel: also known as "pea shingle" is clean gravel similar in size to garden [[peas]].{{sfn|Jackson|1997|loc="pea gravel"}} Used for concrete surfaces, walkways, driveways and as a substrate in home aquariums.
;Piedmont gravel: a coarse gravel carried down from high places by mountain streams and deposited on relatively flat ground, where the water runs more slowly.{{sfn|Jackson|1997|loc="piedmont gravel"}}
;Plateau gravel: a layer of gravel on a plateau or other region above the height at which stream-terrace gravel is usually found.{{sfn|Jackson|1997|loc="plateau gravel"}}
;Shingle: Coarse, loose, well-rounded, waterworn, specifically [[alluvial]] and [[beach]], sediment that is largely composed of smooth and spheroidal or flattened pebbles, cobbles, and sometimes small boulders, generally measuring {{convert|20 to 200|mm}} in diameter.{{sfn|Jackson|1997|loc="shingle"}}

==Relationship to plant life==
In locales where gravelly soil is predominant, plant life is generally more sparse.<ref>C.Michael Hogan. 2010. [http://www.eoearth.org/article/Abiotic_factor?topic=49461 ''Abiotic factor''. Encyclopedia of Earth. eds Emily Monosson and C. Cleveland. National Council for Science and the Environment] {{webarchive|url=https://web.archive.org/web/20130608071757/http://www.eoearth.org/article/Abiotic_factor?topic=49461 |date=8 June 2013 }}. Washington DC</ref> This is due to  the inferior ability of gravels to retain moisture, as well as the corresponding paucity of mineral nutrients, since finer soils that contain such minerals are present in smaller amounts.

==In the geologic record==
[[Sediment]]s containing over 30% gravel that become [[lithification|lithified]] into solid rock are termed [[conglomerate (geology)|conglomerate]].<ref name=BlattTracy/> Conglomerates are widely distributed in [[sedimentary rock]] of all ages, but usually as a minor component, making up less than 1% of all sedimentary rock.<ref name=Boggs/> [[Alluvial fans]] likely contain the largest accumulations of gravel in the geologic record.<ref name="leeder-2011-282-294">{{cite book |last1=Leeder |first1=Mike |title=Sedimentology and sedimentary basins : from turbulence to tectonics |date=2011 |publisher=Wiley-Blackwell |location=Chichester, West Sussex, UK |isbn=9781405177832 |pages=290 |edition=2nd}}</ref> These include conglomerates of the Triassic basins of eastern North America and the [[New Red Sandstone]] of south [[Devon]].<ref name="blatt-etal-1980-629-632" />

==See also==
* [[Construction aggregate]]
* [[Melon gravel]]
* [[Pebble]]
* [[Rock (geology)|Rock]]
*[[Shingle beach]]

==References==
{{Reflist}}

==External links==
{{Commons category-inline|Gravel}}
* {{cite EB1911|author=Flett, John Smith|author-link=John Smith Flett|wstitle=Gravel|volume=12|page=382}}
** {{cite web|title="Gravel", ''Encyclopedia Britannica'' 11th edition, Short Nonfiction Collection, Vol. 041, Section 6 (reader VfkaBT)|website=[[LibriVox]]|url=https://ia600203.us.archive.org/26/items/nonfiction041_1602_librivox/snf041_gravel_flett_mp_128kb.mp3}}
* [https://earthwise.bgs.ac.uk/index.php/Category:Understanding_coastal_protection_by_gravel_barriers_in_a_changing_climate British Geological Survey UKGravelBarriers: Understanding coastal protection by gravel barriers in a changing climate]

{{Geotechnical engineering|state=collapsed}}
{{Authority control}}

[[Category:Aggregate (composite)]]
[[Category:Sedimentology]]
[[Category:Building stone]]
[[Category:Natural materials]]
[[Category:Pavements]]
[[Category:Gardening aids]]
[[Category:Stone (material)]]
[[Category:Soil-based building materials]]