Editing Clay (section)

== Varieties ==
The main groups of clays include [[kaolin]]ite, [[montmorillonite]]-[[smectite]], and [[illite]]. [[Chlorite group|Chlorite]], [[vermiculite]],{{sfn|Nesse|2000|p=253}} [[talc]], and [[pyrophyllite]]{{sfn|Klein|Hurlbut|1993|pp=514-515}} are sometimes also classified as clay minerals.  There are approximately 30 different types of "pure" clays in these categories, but most "natural" clay deposits are mixtures of these different types, along with other weathered minerals.{{sfn|Klein|Hurlbut|1993|p=512}} Clay minerals in clays are most easily identified using [[Clay mineral X-ray diffraction|X-ray diffraction]] rather than chemical or physical tests.{{sfn|Nesse|2000|p=256}}

[[Varve]] (or ''varved clay'') is clay with visible annual layers that are formed by seasonal deposition of those layers and are marked by differences in [[erosion]] and organic content. This type of deposit is common in former [[glacial lake]]s. When fine sediments are delivered into the calm waters of these glacial lake basins away from the shoreline, they settle to the lake bed. The resulting seasonal layering is preserved in an even distribution of clay sediment banding.{{sfn|Foley|1999}}

[[Quick clay]] is a unique type of [[marine clay]] indigenous to the glaciated terrains of [[Norway]], [[North America]], [[Northern Ireland]], and [[Sweden]].{{sfn|Rankka|Andersson-Sköld|Hultén|Larsson|2004}} It is a highly sensitive clay, prone to [[Soil liquefaction|liquefaction]], and has been involved in several deadly [[landslide]]s.{{sfn|Natural Resources Canada|2005}}