The word manganites is playable in Words With Friends™, no blanks required. Because it is longer than 7 letters, you would have to play off an existing word or do it in several moves.
Words With Friends™ Letter Score: 17
Highest Scoring Words With Friends™ Play In The Letters
Seven Letter Word Alert: (29 words)
against, agatine, agatise, amentia, amnesia, anginas, animate, antigen, enigmas, gamiest, gateman, gentian, inmates, magenta, magnate, magnets, manages, matings, meaning, mintage, nametag, nesting, seaming, seating, sigmate, stamina, teaming, teasing, tensing