smectite
noun
smec·tite ˈsmek-ˌtīt 
: montmorillonite
smectitic
(ˌ)smek-ˈti-tik
adjective 
Word History
Etymology
smectis fuller's earth, modification of Greek smēktris kind of fuller's earth, from smēchein to clean
First Known Use
1811, in the meaning defined above