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a clay mineral of the silicate class having a complex chain-lattice structure. Its chemical composition is Mg4[Si6O15](OH)2·6H2O. Mg can be replaced by Fe2+. Fe3+, Ni, Al, and Cu (varieties: ferrisepiolite, aluminosepiolite, and nickelsepiolite). Sepiolite is thought to crystallize in the ortho-rhombic system, forming fibrous submicroscopic crystals. Its properties are analogous to those of palygorskite, and it also occurs as compact or spongy aggregates of very light weight (meerschaum). Sepiolite is formed in soils under conditions of an arid or semiarid climate, in sea and saline basins, and among sedimentary argillaceous carbonate rocks. It is also formed from the weathering of serpentine masses. Varieties of sepiolite rich in nickel are components of silicate nickel ores.