smektiittityypit

Smektiitti (Finnish: smektiitti) is the Finnish term for the smectite group of clay minerals, belonging to the phyllosilicate class. Smectites are characterized by a layered silicate structure that allows interlayer cations and water molecules to expand and contract. This unique structure gives smectites their notable swelling, plasticity, and ion‑exchange capacity. The group is polytypic and includes several rock‑forming members, among which the most commonly studied types are montmorillonite, beidellite, nontronite, and saponite. Montmorillonite is the prototypical Smectite, distinguished by its high sodium or calcium content and high swelling capacity, and it is widely distributed in marine and lacustrine sediments, as well as in volcanic ash layers. Beidellite contains more aluminium in the octahedral sheet and typically shows a higher aluminium-to-magnesium ratio, making it more common in alkaline soils. Nontronite contains iron in the octahedral sheet, giving it a characteristic green hue; it occurs mainly in oxidized sulfate mine tailings and paleosols. Saponite, though less common, has a mixed Mg–Fe hydroxyl layer and is often found in weathered feldspar deposit areas.

Smectite minerals are used extensively in drilling muds, as a binder in foundry sands, as a catalyst support, and as a base material for various engineered composites. In geotechnical engineering, their swelling properties must be considered for foundations, embankments, and nuclear waste containment. In addition, smectites are employed in the adsorption of water and pollutants, in the preparation of pharmaceutical dosage forms, and in soil conditioning. The diversity of their chemical composition, layering, and interlayer cations leads to a wide range of physical and chemical properties that make smectites subjects of active research in mineralogy, materials science, and environmental engineering.