The word plagioclase 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: 21
Highest Scoring Words With Friends™ Play In The Letters plagioclase
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Seven Letter Word Alert: (25 words)
alcogel, apogaic, apogeal, apogeic, callose, celosia, coalise, collage, collies, epilogs, gallops, gelcaps, glacial, goalies, locales, logical, paellas, palaces, pelagic, pillage, polices, scallop, scalpel, spacial, special