What is an alluvium in geology ?

Alluvium : definition

Alluvium is the sediment of rivers and beaches ; composed of detritic fragments with variable particle size and often with very heterogeneous lithology, all the rocks present on a catchment area can be eroded and transported in alluvial deposits.
 
Alluvium consists of clay and silt (fine fraction), sand (medium fraction), gravel, pebbles and blocks (large fraction). These deposits can constitute mineral resources : aggregates (gravel, sands), sometimes heavy minerals (gold, cassiterite, rutile...).
 
The term alluvial deposit (or placer) is usually reserved for alluvium containing sufficient quantities of useful minerals or ores (gold, platinum, diamond, sapphire, rutile, kaolin...) to justify extraction. These placers are formed by mechanical sorting operated by water in alluvial streams or on beaches. In the latter case they are often referred to as black sands (due to the dominance of black minerals such as ilmenite or magnetite for example), or red sands (dominance of garnets).

ReCaptcha

This service is used to secure web forms of our website and required if you want to contact us. By accepting it you agree to Google's privacy policy: https://policies.google.com/privacy

Facebook

Our website allows you to like or share its content on Facebook social network. By activating and using it you agree to Facebook's privacy policy: https://www.facebook.com/policy/cookies/

YouTube

Integrated videos provided by YouTube are used on our website. By accepting to watch them you agree to Google's privacy policy: https://policies.google.com/privacy

Twitter

Integrated tweets and share services of Twitter are used on our website. By accepting and using these you agree to Twitter's privacy policy: https://help.twitter.com/en/rules-and-policies/twitter-cookies

PInterest

Our website allows you to share its content on PInterest social network. By activating and using it you agree to PInterest's privacy policy: https://policy.pinterest.com/en/privacy-policy/