Mephedrone in aqueous and acidic solutions gives composites of thick, irregular tablets. These crystal are very bright under crossed polars with different parts of the composite going extinct at different times on rotation of the stage. The size and thickness of the crystals makes them suitable for infrared microspectroscopy. The spectra obtained in transmission mode are information rich. They are representative of the mephedrone molecular structure while accounting for the shifts caused by mephedrone interaction with reagent.