Furanyl fentanyl forms clusters of thin, colorless plates with the platinic chloride reagent. The crystal habit differs between the aqueous, 10% hydrochloric acid, and 10% acetic acid solutions. The largest and most reliable crystals are formed with 10% hydrochloric acid. In water, the individual crystals in the cluster are a mix of narrow rod-like structures and light feathery plates. The clusters in 10% hydrochloric acid are larger with a mix of short and long plates. The clusters get tighter with short and broad plates in 10% acetic acid. All three forms of the crystals appear bright under crossed polars.
The acetic acid solution crystals are amenable for IR microspectroscopy but the quality of the spectra is not very good.