The word magnesites 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: 16
Highest Scoring Words With Friends™ Play In The Letters
Seven Letter Word Alert: (45 words)
easiest, enigmas, gametes, gamiest, gatemen, genesis, ingests, inmates, inseams, magnets, massing, matinee, matings, meanest, meanies, meeting, menages, message, messing, mintage, misseat, negates, nemesis, sagiest, sateens, seaming, seating, seeming, segment, seitans, seitens, senates, sensate, sestina, sestine, siamese, siemens, sigmate, signees, signets, stamens, stigmas, teaming, teasing, teeming