The word gritstones 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: 13
Highest Scoring Words With Friends™ Plays In The Letters
Seven Letter Word Alert: (46 words)
egoists, egotist, engross, goiters, goitres, goriest, ignores, ingests, ingress, inserts, intorts, norites, nosiest, notists, orients, regions, resigns, resting, retints, rosiest, rotting, seniors, setting, signers, signets, signors, singers, sinters, sitters, snotter, sorties, sorting, stetson, stinger, stogies, stoners, stonier, stories, storing, strings, tensors, testing, tigress, tinters, tossing, triones