The word cassiterite 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: 14
Highest Scoring Words With Friends™ Plays In The Letters
Seven Letter Word Alert: (52 words)
actress, aeriest, airiest, artiest, artists, ascites, attires, casters, cattier, cerates, cerises, citrate, creases, creates, cresset, cristae, easiest, estates, iratest, irisate, iterate, raciest, racists, recasts, recites, reseats, resects, restate, retaste, retests, satires, satiric, scatter, seaters, secrets, seriate, setters, sitters, staters, statice, statics, straits, streets, striate, tasters, tastier, teasers, tersest, testers, testier, trisect, tsarist