4-FluoroBZP when dissolved in acidic solutions forms feathery blades. With 10% hydrochloric acid, the branched blades are more prominent. The blades are very faint in crossed polars. With 10% acetic acid, a combination of feathery blades and ribbons are observed. The ribbons are very bright under crossed polars.
Platinic chloride forms two types of crystals with 4-FluoroBZP. The long branched sheaves of dark crystals appear faint under crossed polars. The second form of crystals are thick hexagonal crystals that grow in straight or branched chains. The hexagons are very distinct and appear very bright under crossed polars. This test is very sensitive and crystals form reliably.