glau·co·nite 
(glôkə-nīt′)
(glôkə-nīt′)n.
A greenish mineral of the mica group, a hydrous silicate of potassium, iron, aluminum, or magnesium, (K,Na)(Al,Fe,Mg)2(Al,Si)4O10(OH)2, found in greensand and used as a fertilizer and water softener.
[German Glaukonit : Greek glaukon, neuter of glaukos, gray + -ITE1.]
glau′co·nitic (-nĭtĭk) adj.