  We report a simple route to form robust, inorganic, semi-permeable
compartments composed of montmorillonite, a natural plate-like clay mineral
that occurs widely in the environment. Mechanical forces due to shear in a
narrow gap assemble clay nanoplates from an aqueous suspension onto air
bubbles. Translucent vesicles suspended in a single-phase liquid are produced
when the clay-covered air bubbles are exposed to a variety of water-miscible
organic liquids. These vesicles of clay are mechanically robust and are stable
in water and other liquids. The formation of clay vesicles can be described by
a physical mechanism that recognizes changes in the wetting characteristics of
clay-covered air bubbles in organic liquids. The clay vesicles are covered with
small pores and so intrinsically exhibit size-selective permeability, which
allows spontaneous compartmentalization of self-assembling molecules in aqueous
environments. The results we report here expand our understanding of potential
paths to micro-compartmentalization in natural settings and are of relevance to
theories of colloidal aggregation, mineral cycles, and the origins of life.
