Noun
A hydrous silicate of alumina, of a greenish color, which, in certain states of humidity, appears transparent and almost gelatinous.
Source: Webster's dictionaryElectron microscope photograph of smectite clay – magnification 23,500 Clays are distinguished from other fine-grained soils by differences in size and mineralogy. Source: Internet
Kimberlite deposits are known as blue ground for the deeper serpentinized part of the deposits, or as yellow ground for the near surface smectite clay and carbonate weathered and oxidized portion. Source: Internet