| an extraordinary or unusual thing, person, or event; an exceptional example or instance. |
| a chattering or flighty, light-headed person. |
montmorillonite
any of a group of clay minerals and their chemical varieties that swell in water and possess high cation-exchange capacities. The theoretical formula for montmorillonite (i.e., without structural substitutions) is (OH)4 Si8 Al4 O20nH2 O.
Learn more about montmorillonite with a free trial on Britannica.com.