The Collaborative International Dictionary
Hydromica schist
Hydromica \Hy`dro*mi"ca\, n. [Hydro-, 1 + mica.] (Min.) A variety of potash mica containing water. It is less elastic than ordinary muscovite.
Hydromica schist (Min.), a mica schist characterized by the presence of hydromica. It often has a silky luster and almost soapy feel.