Editing Gravel (section)

==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>