saponite

Saponite is a trioctahedral clay mineral in the smectite group, characterized by a 2:1 layered silicate structure. Like other smectites, its structure consists of two tetrahedral sheets enclosing an octahedral sheet; the layers stack to form expandable interlayers that accommodate water and exchangeable cations. In saponite, the octahedral sheet is predominantly occupied by magnesium (and iron in some varieties), giving it a trioctahedral character. The overall layer charge results mainly from substitutions in the tetrahedral framework, and is balanced by interlayer cations such as sodium, calcium, or potassium. This composition gives saponite a relatively high cation exchange capacity and strong swelling upon hydration.

Saponite occurs in a variety of geological settings, including weathering products of magnesium- and iron-rich rocks, altered ultramafic rocks, volcanic ash deposits, and some hydrothermal environments. It is commonly found in soils and sedimentary deposits, where it contributes to the plasticity, water retention, and nutrient-holding capacity of the clay fraction. The mineral typically forms platy, flaky aggregates and can range in color from white to greenish or yellowish.

Because of its expandable structure and high surface area, saponite is useful in several applications. It is employed as a component of drilling fluids, as a soil amendment to improve moisture retention and cation exchange properties, and as an adsorbent and filler in ceramics and environmental cleanup contexts. The name “saponite” derives from the soapy feel of the clay when wet, a characteristic noted in its early descriptions.