In this case, rockbridgeite is a ferrous iron rich mineral and frondelite is the manganese rich member of the series. Color is brown, dark green, yellow-brown or black. Luster is varied from vitreous to dull or earthy. Specimens are translucent to transparent. Crystal Habits include prismatic to tabular crystals, but often botryoidal, reniform, encrusting, massive and fibrous.
Cleavage is poor.
Fracture is uneven. Streak is green or brown. Associated Minerals include strengite , beraunite , dufrenite and limonite . Best Field Indicators are crystal habit, color, associations and streak.