Saponite is a trioctahedral of the smectite group. Its chemical formula is Ca0.25(Mg,Fe)3((Si,Al)4O10)(OH)2·n(H2O). It is soluble in sulfuric acid. It was first described in 1840 by Svanberg. Varieties of saponite are griffithite.
It is soft, massive, and plastic, and exists in veins and cavities in serpentinite. The name is derived from the Greek. Other names include bowlingite; mountain soap; piotine.