sauconite

Sauconite is a rare zinc- and aluminium-rich hydrous phyllosilicate mineral in the smectite group. It forms as a layered 2:1 clay mineral with tetrahedral silica sheets and octahedral sheets containing zinc and aluminum, and with interlayer water and exchangeable cations. The composition varies with locality, but zinc and aluminium are dominant, and silicon and oxygen complete the structure. Like other smectites, sauconite exhibits a negative layer charge and a significant capacity to swell by adsorbing water and exchangeable ions.

Discovery and name: Sauconite was first described from Saucon Valley in Pennsylvania, USA, and the name derives from that locality. The mineral is named for its zinc-rich composition and its type locality.

Occurrence and associations: Sauconite occurs in hydrothermal and weathering environments where zinc-bearing rocks are present, often in ore-related environments with secondary zinc minerals. It is reported from zinc-rich veins and contact zones and is commonly associated with smithsonite, hemimorphite, goethite, and calcite.

Physical properties and significance: Sauconite is typically pale green to brown and has an earthy to platy habit. It is soft (Mohs 2–3) and has a low to moderate specific gravity (about 2.3–2.6). It lacks widespread commercial use but is studied for mineralogical and geological purposes, particularly in understanding the aging of zinc-bearing ore systems and the behavior of clays in hydrothermal environments.