Class : Silicates
    Subclass : Phyllosilicates
    Crystal system : Monoclinic
    Chemistry : X_0.3Y_2-3Z₄O₁₀(OH)₂ nH₂O
    Rarity : Very common

Smectite is the name given to a group of monoclinic phyllosilicates that are related to clays. Its name comes from the Greek smêktikos (to clean) in allusion to its soapy appearance. It is formed overwhelmingly by meteoric alteration of aluminum silicates, especially feldspars. This group is usually divided according to the filling of the octahedral sites, into di-octahedral smectites (of which the most common members are montmorillonite, beidellite and nontronite) and tri-octahedral smectites (including saponite and hectorite). The interlayer spaces of smectites are occupied by large cations (K, Na, etc...) and water molecules. The spacing between two layers varies from 9.6 angstroms when the smectite is dry to 18 angstroms when it is saturated with water. This ability to retain water trapped between the layers is one of the major mechanisms of water retention in soils. It is obviously an absolutely essential property for the development of plant life and therefore agriculture, but it is also responsible for cracking of buildings during droughts.

Main photo : Smectite in mud-cracks

No fakes listed for this mineral species.