From the scholia to Aristophanes, Frogs 712, where the headword occurs (web address 1). Named from the island of Cimolus/Kimolos (kappa 1619). See also kappa 1744, kappa 2640.
This earth, often used as fuller's earth, is a kind of clay of the montmorillonite group, also today called cimolite. It is a hydrated aluminum silicate and the crystal lattice has three lathlike layers: one sheet of aluminum groups between two sheets of silicate oxide, with water molecules as a weak bond between the layers. There may be calcium, chloride or potassium ions dissolved in the water layer. All these components mean that there is a possibility for ion exchange; it has bleaching properties as well as a propensity for high level absorptive power. These factors make the compound very useful as a detergent or soap and was often used as such through much of antiquity. [Note courtesy Carl Widstrand.] See Encyclopedia Brittanica entry at web address 2.
Soap is mentioned also at rho 303 and sigma 101.