montmorilloniit

Montmorillonite is a clay mineral in the smectite group. It is a 2:1 layered silicate, consisting of a central octahedral sheet sandwiched between two tetrahedral sheets. Negative charge in the layers arises from isomorphous substitution, such as Al3+ for Si4+ in the tetrahedral sheets or Mg2+ for Al3+ in the octahedral sheet. This charge is balanced by exchangeable interlayer cations such as Na+, Ca2+, or K+. The structure gives montmorillonite a high cation exchange capacity and a pronounced ability to take up water, causing swelling.

Montmorillonite-rich clays are typically very plastic when wet and form a cohesive solid upon drying. They exhibit significant swelling with hydration and have low frictional resistance when wet, properties that make them useful in drilling muds, grouts, and as barrier materials in civil engineering. They also act as effective adsorbents for contaminants and have applications in cosmetics, pharmaceuticals, ceramics, and environmental remediation.

Formation commonly occurs by alteration of volcanic ash (tuff) or feldspathic rocks, leading to the development of smectite minerals. Montmorillonite is a dominant component of bentonite, a clay with high montmorillonite content. The mineral is named after Montmorillon, a locality in France where it was first described in the 19th century.

In summary, montmorillonite is a swelling, high-CEC clay mineral of the smectite group, with broad industrial and environmental applications and a geological origin linked to volcanic and feldspathic rock weathering.